Nurve Networks HYDRA SD MAX User manual

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HYDRA™ SD MAX Storage Card User Manual v1.0 (SAMPLE)
Copyright © 2008 Nurve Networks LLC
Author
Andre’ LaMothe
Editor/Technical Reviewer
The “Collective”
Printing
0001
ISBN
Pending
All rights reserved. No part of this user manual shall be reproduced, stored in a retrieval system, or transmitted by any means,
electronic, mechanical, photocopying, recording, or otherwise, without written permission from the publisher. No patent
liability is assumed with respect to the user of the information contained herein. Although every precaution has been taken in
the preparation of this user manual, the publisher and authors assume no responsibility for errors or omissions. Neither is any
liability assumed for damages resulting from the use of the information contained herein.
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All terms mentioned in this user manual that are known to be trademarks or service marks have been appropriately
capitalized. Nurve Networks LLC cannot attest to the accuracy of this information. Use of a term in this user manual should
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Every effort has been made to make this user manual as complete and as accurate as possible, but no warranty or fitness is
implied. The information provided is on an “as is” basis. The authors and the publisher shall have neither liability nor any
responsibility to any person or entity with respect to any loss or damages arising from the information contained in this user
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programs are copyrighted by their respective owners and may require separate licensing.

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Licensing, Terms & Conditions
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HYDRA SD Max Storage Card User Manual Sample
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Version & Support/Web Site
This document is valid with the following hardware, software and firmware versions:
•HYDRA Game Console Revision A. or greater.
•Propeller Tool 1.0 or greater.
The information herein will usually apply to newer versions but may not apply to older versions. Please contact Nurve
Networks LLC for any questions you may have.
Visit www.xgamestation.com for downloads, support and access to the XGameStation/HYDRA user community and
more!
For technical support, sales, general questions, share feedback, please contact Nurve Networks LLC at:
[e-mail] / nurv[email protected]

HYDRA SD Max Storage Card User Manual Sample
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Table of Contents
LICENSING, TERMS & CONDITIONS ................................................................................................................................... 3
VERSION & SUPPORT/WEB SITE........................................................................................................................................ 4
TABLE OF CONTENTS .......................................................................................................................................................... 5
HYDRA SD MAX+128K CARD USER MANUAL.................................................................................................................... 6
1.0 HYDRA SD MAX STORAGE CARD MANUAL OVERVIEW ............................................................................................ 6
2.0 PRODUCT CONTENTS.................................................................................................................................................... 7
2.1 CD-ROM CONTENTS ...................................................................................................................................................... 7
3.0 INTRODUCTION AND QUICK START............................................................................................................................. 8
3.1 QUICK START GUIDE ..................................................................................................................................................... 10
3.1.1 Re-programming the HYDRA SD Max Card with the Menu Demo Program ..10
3.1.2 Re-formatting the SD Card with the Demo Binary Images..............................11
4.0 CIRCUIT DESIGN, ELECTRICAL AND MECHANICAL INTERFACE............................................................................ 12
4.1 ELECTRICAL INTERFACE DESIGN .................................................................................................................................... 12
4.2 MECHANICAL INTERFACE ............................................................................................................................................... 15
5.0 INTERFACING TO THE HYDRA SD MAX CARD..........................................................................................................16
5.1 SD CARD OVERIEW &HISTORY ..................................................................................................................................... 17
5.2 SPI BUS BASICS ........................................................................................................................................................... 18
5.2.1 Basic SPI Communications Steps...................................................................20
5.3 SD CARD COMMUNICATIONS PROTOCAL ........................................................................ERROR!BOOKMARK NOT DEFINED.
5.3.1 Placing the SD Card into SPI Mode ..................Error! Bookmark not defined.
5.3.2 Reading a Sector...............................................Error! Bookmark not defined.
5.3.3 Writing a Sector .................................................Error! Bookmark not defined.
5.4 FAT16 FILE SYSTEM OVERVIEW....................................................................................ERROR!BOOKMARK NOT DEFINED.
5.4.1 FAT16 SD Card Disk Structure .........................Error! Bookmark not defined.
5.4.2 Master Boot Record ..........................................Error! Bookmark not defined.
5.4.3 Partition Entries in the MBR ..............................Error! Bookmark not defined.
5.4.4 Parition Boot Record (PBR) ..............................Error! Bookmark not defined.
5.4.5 A Quick Recap and Locating the Primary FAT16 Data StructuresError! Bookmark not defined.
5.4.6 The Root Directory ...........................................Error! Bookmark not defined.
5.4.7 The File Allocation Table...................................Error! Bookmark not defined.
5.4.8 Understanding Directories.................................Error! Bookmark not defined.
5.4.9 Final Aspects of Navigating the FAT16 File SystemError! Bookmark not defined.
6.0 UNLEASHING THE SD MAX DRIVER API ........................................................ ERROR! BOOKMARK NOT DEFINED.
6.1 Driver API Constants ............................................Error! Bookmark not defined.
6.2 Driver API Globals ................................................Error! Bookmark not defined.
6.3 Initializing the SD Max Driver ...............................Error! Bookmark not defined.
6.4 Master API Listing ................................................Error! Bookmark not defined.
7.0 THE HYDRA SD MAX DEMOS .......................................................................... ERROR! BOOKMARK NOT DEFINED.
7.1 THE MENU LOADER PROGRAM.......................................................................................ERROR!BOOKMARK NOT DEFINED.
7.1.1 The Menu Loader Software Architecture ..........Error! Bookmark not defined.
7.1.2 Building the SD Card for the Loader .................Error! Bookmark not defined.
7.2 THE SD MAX DEMO API PROGRAM...............................................................................ERROR!BOOKMARK NOT DEFINED.
7.2.1 The Main Menu..................................................Error! Bookmark not defined.
8.0 SUMMARY.......................................................................................................... ERROR! BOOKMARK NOT DEFINED.
APPENDICES ........................................................................................................... ERROR! BOOKMARK NOT DEFINED.
A. HYDRA SD MAX SCHEMATIC .........................................................................................ERROR!BOOKMARK NOT DEFINED.
B. PCB REFERENCE LAYOUT ..............................................................................................ERROR!BOOKMARK NOT DEFINED.
C. API DRIVER SOURCE CODE LISTING................................................................................ERROR!BOOKMARK NOT DEFINED.
NOTES.............................................................................................................................................................................. 22

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HYDRA SD Max+128K Card User Manual
1.0 HYDRA SD Max Storage Card Manual Overview
Welcome to the user manual for the HYDRA SD Max Storage Card. The HYDRA SD Max Storage Card or “SD Max”
for short, enhances the functionality of the HYDRA by adding the ability to read and write standard SD (Secure Digital)
cards. The hardware interface is facilitated by a standard HYDRA expansion card with a SD card slot built in as well as a
128K EEPROM for program storage. The hardware interface exports lines for both SPI (serial peripheral interface) mode
as we as proprietary SD mode (assuming you have a license).
Thus, you can use simple SPI routines to talk to the SD card or if you are a licensed SD card developer you can access
the card at high speed. Also, you can always find “educational” notes on internet on how to access the high speed modes
and then write code to do so, but if you every produce a consumer product with the high speed protocol you better have a
license, or you might get a visit from the “SD Police”. However, for the demos and drivers within we will stick with the free
SPI modes of SD card operation.
The HYDRA SD Max Storage Card not only has the SD card interface on it, but comes with a standard 128K serial
EEPROM chip on-board, so that you can load your applications onto the 128K EEPROM and boot from the card as well.
Thus, the card doubles as a 128K EEPROM memory expansion card when you’re not interested in using the SD slot.
NOTE
The high speed modes of the SD card interface is not free to use. There are two modes of operation; SPI
mode and SD mode. In SPI mode there are no royalties, but in SD modes you must pay a fee to license to
use (there are two version 1-bit and faster 4-bit protocol). Read more about it here:
http://en.wikipedia.org/wiki/Sd_card. However, 99% of hobby or educational products simply use the SPI
mode which is more than adequate.
There is a lot you need to know to write software yourself to access SD cards. From the bottom up, first, there is the
electrical interface to the SD card itself which is a number of signals and power, then the actual communications to the
device is based on the SPI (serial peripheral interface) which is a 3-line serial protocol (data in, data out, clock) in SPI
mode of course. That’s how you talk to the SD card. Then on top of that you need to send the SD card commands in SD
protocol format. This gives you access to the card’s features, but not the file system. You can read and write sectors, but
they are in raw form. If you want to really take advantage of the SD card then you have to emulate the DOS FAT16 (or
FAT32) file system standard. Alas, you have to write a version of the FAT16 file system on the HYDRA to access the
card!
This is a lot of work no doubt, but hopefully this manual will give you insight into how to do this yourself. And of course, I
will provide pre-made drivers and an API written in SPIN for ease of understanding along with a little menu driven demo.
Nevertheless, I highly recommend that you try and conquer everything from the electrical interface, the SPI protocol, the
SD card protocol and FAT16, so you know every single bit (no pun intended) of operation of these amazing little storage
devices. The ability to hold 4Gigs in something the size of a stamp is amazing when you think about it. Assuming a page
of text is about 4000 characters and the average book 350 pages, that means that a 4Gig SD card can hold
4,000,000,000 / 350 * 4000 = 2857 books!!!! So you could easily store everything we know about math, physics,
computers, electronics, chemistry, biology easily along with arts and a good helping of fiction if it was the end of the world
and you had to leave the planet and could only take what you could fit in your pockets!

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Figure 1.0 – The HYDRA SD Max Storage Card and Accessories.
2.0 Product Contents
The HYDRA SD Max Storage Card kit consists of the following items as shown in Figure 1.0:
The HYDRA SD Max Storage Card itself with SD card slot and 128K EEPROM onboard.
A 1GB SD card pre-formatted with a FAT16 file system (SD card may very from model shown).
CD-ROM with source, tools, API, etc. (not shown).
Printed Quick Start Sheet (not shown).
NOTE
The 1GB SD card that comes with the kit is pre-format FAT16 and has a file system on it with a
number of binaries for the pre-programmed demo that comes on the SD cards. You can erase and
re-format the SD card at any time.
2.1 CD-ROM Contents
The CD-ROM contains the documentation, drivers, demos, and all source code for the SD Max. Additionally, there is a
bonus sub-directory with the latest HYDRA demos and software that are user submitted. The CD-ROM layout is as
follows:
CD_ROM:\ README.TXT
AUTORUN.SYS
LICENSE.TXT
SOURCES\
\SD_MENU_IMAGE
SCHEMATICS\
DOCS\
\DATASHEETS
\FAT
\SD
\SPI
TOOLS\
GOODIES\
NOTE: “CD_ROM” is your CD-ROM drive letter; “D:”, “E:”, etc.

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Figure 2.0 – Annotated close up of the HYDRA SD Max Storage Card.
3.0 Introduction and Quick Start
A close-up of the HYDRA SD Max Storage Card shown in Figure 2.0. The SD Max card has a simple friction type front
loading standard SD card slot that accepts “standard” size SD cards (mini and micro cards can be used with adapters).
The SD Max card also has a 128K serial EEPROM on it, so SD card programs can be stored directly on the card and not
need to be loaded separately into the HYDRA’s base board 128K EEPROM.
Additionally, the card has 3 LED indicators:
Power.
Write Protect.
Card Inserted.
Both the signals write protect and card inserted are actually interfaced to the I/O pins of the HYDRA’s expansion slot as
well to help determine these if the inserted card is write protected, or that a card is inserted at all. The SD card can be
queried as well with software techniques to determine if its inserted and if so write protected, but having the extra
signals makes life a little easier.
The main idea of the SD card is augment the HYDRA with a complete file system for loading and storing large amounts of
data. The SD card format is perfect since the hardware interface is very modest (only 3 lines needed in SPI mode). And
the speed is quite respectable at 25MHz even in license free SPI mode. The circuit design (discussed in the next
section) supports high speed 4-bit modes as well for users that want to experiment with the other SD card modes for non-
commercial applications.

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Figure 3.0 – A simplified illustration of the SD Max software model.
The software interface to the SD card is a layered model as shown in Figure 3.0. At the lowest level there is a SPI driver
which does nothing except send and receive bytes to and from the SD card. On top of this protocol is the SD SPI mode
protocol which can be used to completely control the SD card as well as read/write “sectors”. But, to interface the cards
with the PC and be able to transparently swap the card from the PC to the HYDRA, a FAT16 file system is needed since
that’s what the PC uses to format and access the SD card. Thus, we need yet one more layer on top of the SD card
protocol that implements FAT16 which is no easy feat.
NOTE
FAT16 is a file system used on DOS and Windows PCs, originally introduced in 1987 as a successor
to the FAT12 system for floppy drives. FAT16 is simply a method of organizing a hard drive or floppy
disk into sectors, clusters, and a directory system that allows a file system to be efficiently developed
to access files, read and write. More on the FAT16 system later in the manual. A good overview can
be found here: http://en.wikipedia.org/wiki/File_Allocation_Table.
The SD card can be used for all kinds of applications from simple file storage to virtual memory and advanced media
applications. Later in the summary some ideas about cool things to do with the SD card will be discussed.
Figure 4.0 – Inserting the HYDRA SD Max card into the HYDRA.

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3.1 Quick Start Guide
The HYDRA SD Max card’s 128K EEPROM is pre-loaded with a little demo program that lists a number of demo,
programs, games, and applications that you can scroll thru and select and load into the HYDRA and run as shown in
Figure 5.0 below. If you are an old Atari, Commodore 64, or Apple programmer this will look very familiar to the old
loaders that used to boot and give you a selection of games to play!
This functionality is accomplished by an SD card reader driver coupled with software that allows Propeller 32K EEPROM
“images” with extension .EEPROM to be loaded directly into SRAM and then the Propeller to be re-booted. A binary
image is simply a 32K byte image that is the result of compiling a standard SPIN/ASM program.
The demo binary images that the demo uses are pre-loaded onto the SD card’s root directory, so all you have to do is
insert the SD card itself into the HYDRA SD Max card slot and then insert the HYDRA SD Max card into the HYDRA itself.
This is shown in Figure 4.0. Of course, you can hot slot the SD card itself (as well as the HYDRA SD Max card), thus, first
you can insert the HYDRA SD Max card into the HYDRA and then insert the SD card into the SD card acceptor on the
HYDRA SD Max card. Here are the steps to play with the pre-loaded demo and games on:
Step 1. With the HYDRA hooked up to power, TV and the PC, simply insert the SD Max card into the expansion
slot facing the front of HYDRA as shown in Figure 4.0, be careful not to force it. The HYDRA can be on or off.
Make sure you have the game controller in the left controller port of the HYDRA.
Step 2. Turn the HYDRA on and/or reset it and the card should reset and boot up the test suite. You will see the
power LED on the top-left of the card light up as shown in Figure 4.0. If the SD Max card doesn’t boot, leave the
power on and simply remove and re-insert the card to get a better insertion connection and try hitting reset.
Step 3. You should see the demo menu on screen as shown in Figure 5.0, use the up/down directional arrows on
the game controller to scroll thru the demos, once you find something that sounds interesting press the Start
button, the demo will load. When you want to try another demo, simply reset the HYDRA with the Reset button.
Figure 5.0 – The pre-loaded SD loader menu.
If you don’t see the menu or the menu shows no programs available to load then either the pre-programmed demo
program on the 128K EEPROM needs re-programming, or the SD card needs re-flashing. Refer to the sections below for
steps to restore your product.
3.1.1 Re-programming the HYDRA SD Max Card with the Menu Demo Program
With the HYDRA SD Max card inserted into the HYDRA, simply load the program on the CD named MENU_001.SPIN
located here:
CD_ROM:\sources\menu_001.spin
and write it to the 128K EEPROM on the HYDRA SD Max card with F11 from the Propeller IDE. This should refresh the
damaged program.

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3.1.2 Re-formatting the SD Card with the Demo Binary Images
If the demo programs on the SD card get damaged somehow, you simply need to restore the SD card, which is trivial.
You will need an SD card reader plugged into your PC. Then simply plug the SD card into the reader, open the card up
and then inspect the files. You should see a long list of files with various names (each with the .EEPROM file extension)
and a file named DIR.TXT that is used as an internal “directory” for the menu program. If you don’t then chances are the
files got fragged, so you need to re-fresh them. Here are the steps:
Step 1: Format the SD card FAT16. Perform a full format, not a quick format.
Step 2: Locate the folder on the CD in the \Sources directory named \SD_Menu_Images located here:
CD_ROM:\Sources\SD_Menu_Images\
Enter the directory and select all the files and copy them into the SD card. This should re-fresh the card and you are back
in business. Note: You will need to do this anytime you want to play with the SD card menu demo. Since the demo
assumes the card is freshly formatted and has a root copy of all the files on it.
The menu demo is just a taste of what’s possible with the HYDRA SD Max card. You can load potentially thousands of
demos and languages into the HYDRA with a single SD card and never have to remove the card from the HYDRA!
NOTE
The menu program and underlying drivers are based on the hard work of Mike Green’s Femto
BASIC and drivers developed by Tomas Rokicki of Radical Eye Software, they are free for use and
sources available on the CD as well as the Propeller/HYDRA forums and object exchange at
www.parallax.com. The formal HYDRA SD Max driver API written by yours truly is completely in
SPIN for educational reasons, thus once you start really hacking away at the SD card you might want
to use the faster lower level drivers by Mike Green and Radical Eye Software or write your own.
Figure 6.0 – The HYDRA SD Max Storage Card’s electrical design.

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4.0 Circuit Design, Electrical and Mechanical Interface
The HYDRA SD Max card is a very simple design since all of the work is inside the SD card itself. The SD card has a
complete microcontroller, memory, and of course the flash storage all tucked away inside. All we really need to do is
interface to the SPI bus of the SD card via a mechanical SD card holder and that’s about it. If you look at the design in
Figure 6.0, you will see that the HYDRA's expansion bus interface is used to interface to the SD card’s interface. To make
things simple the I/O lines are used for the interface, but in a pinch the networking and I2C lines connected to the
HYDRA’s EEPROM chips could be used, but then it would be hard to implement a complete SD interface. If you recall in
the introductory paragraphs on the SD card there are a few different modes of operation; SPI, 1-bit SD, and 4-bit SD
modes. The various modes use different signals on the SD card’s edge connector, thus, to support future expansion and
more advanced modes the HYDRA’s IO expansion bus is used to implement a complete interface. But, if all you needed
was SPI mode then 3-lines is all you need to do it.
Figure 7.0 – Standard SD card pin labeling (contact side).
4.1 Electrical Interface Design
Referring to Figure 6.0, every single line I/O_0 to I/O_7 is used by the design. However, in SPI mode only a subset of
these lines is necessary. However, to support future expansion into the SD modes of operation, the design connects all
important lines to the HYDRA’s expansion interface. Take a look at Figure 7.0, it depicts the actual SD card physical
interface (if you were looking at the gold fingers). Notice the numbering is left to right, with the last pin, number 9 on the
2nd row, bottom left. You will also notice on Figure 6.0 that the I/O lines all have pull-ups on them. This isn’t 100%
required, but in 1 and 4-bit SD modes its definitely suggested by the SD specification, so we have added them in the
design.
Also, the additional Write Protect and Card Detection signals (I/O_6 and I/O_7) are pulled up as well as ran thru LEDs
for visual indication. The SD card connector will short these lines to ground when the card is inserted or the write protect
is unlocked (see Figure 8.0(b) ), thus the Propeller can read these event on the I/O lines and HIGH or LOW signals
respectively and figure out if a card is in the slot and if its write protected. It’s important to note that write protect and card
detection are NOT part of the SD card’s electrical interface, but simply added to each SD card mechanical slot by the
manufacturer. And therefore, each has their own electrical interface and operation. Thus, to clarify:
Card Inserted Logic
I/O_6 = HIGH when card not inserted, LED off.
I/O_6 = LOW when card is inserted, LED on.
Write Protect Logic
I/O_7 = HIGH when card’s write protect is locked (read only), LED off.
I/O_7 = LOW when card’s write protect is not locked (read/write), LED on.

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That’s about the extent of the electrical design, very simple as you can see. Now, let’s take a look at the actual signals
themselves and see what’s what. Table 1.0 lists the complete electrical interface for all modes of operation of the SD card.
Table 1.0 – SD card interface lines used.
Referring to Table 1.0, depending on the mode of operation the electrical interface of the SD card can change meaning.
For example in SD 4-bit mode pin 8 is data line 1, but in SD 1-bit mode its an interrupt line. Therefore, by exporting all the
lines to the HYDRA’s expansion interface we can write drivers to support the 1-bit and 4-bit modes if we wish. However,
we are more interested in the SPI mode which is shown on the right hand side of the table. In this mode, the interface is a
straight SPI interface consisting of pin 1,2,3,4,5,6, and 7. Pin 8 and 9 are not needed. Also, note that pins 3 and 6 are
ground and 4 is power, so in reality there are only 4 signal lines needed for SPI mode (CS, DI, DO, SCLK).
Nevertheless, we want to support all these modes for experimentation, so we need a connection to every single pin. If you
count up all the signals there are a total of 6 signal lines and 3 power lines. Now, since the HYDRA’s expansion bus has 8
available lines, we still have 2 more signals we can send thru the interface which is perfect for the Card Detect signal and
the Write Protect signal which are implemented on the card slot itself by means of little switches implemented on the
connector itself. That is, when you insert the SD card a short is made which is senses as well as the state of the write
protect tab. But, these signals are not part of the SD card interface and are solely at the discretion of the manufacturer of
the particular SD card slot mechanical you choose for your design. But, we will get to that in a moment.
Right now, let’s take a look at the interface between the SD card signals and the HYDRA expansion port itself. Basically,
we have 6 data signals from the SD card plus 2 extra signals from the mechanical interface itself (indicating card insertion
and write protect tab state) along with the power and grounds. Thus, we have to decide what signal to connect where on
the HYDRA’s I/O_0 to I/O_7 signal lines. This is mostly arbitrary, but I matched them to the most common connections
that people have been using when interfacing SD cards to the HYDRA themselves. Table 2.0 below shows the final
electrical interface from the SD card to the HYDRA expansion interface.
Table 2.0 – SD card interface to HYDRA expansion interface mapping.
SD Card Pin Function Name (EXP/PROP/LOG)
SD 1 (CS/DAT3 - chip select/DAT3) I/O 3 (4/24/P19)
SD 2 (DI/CMD - data in/command) I/O 2 (3/23/P18)
SD 3 GND GND (20)
SD 4 3.3V 3.3V (14)
SD 5 (CLK/SCK – clock/serial clock) I/O 1 (2/22/P17)
SD 6 GND GND (20)
SD 7 (DO/DAT0 - data out/DAT0) I/O 0 (1/21/P16)
SD 8 (DAT1/IRQ) I/O 4 (5/25/P20)
SD 9 (DAT2/NC) I/O 5 (6/26/P21)
Extra Mechanical SD card holder signals not part of the SD interface
SD 10 (1) (CD/Card Detect) I/O 7 (8/28/P23)
SD 11 (1) (WP/Write Protect) I/O 6 (7/27/P22)

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Note 1: SD 10 and 11 are not part of the SD interface, but simply pins that happen to be on the particular SD
card mechanical chosen for the HYDRA SD Max (AVX Inc. makes them). Most SD card slots have similar signals.
The table is a little tricky to read especially in the right most column, so let’s try and example. Let’s trace SD card pin 7
which is the D0 or Data Out line. Starting from the left most column, SD 7’s function is D0 or Data Out. Meaning, in 4-bit
mode its D0 of the 4-bit data, or in 1-bit mode it’s the single “Data Out” line. Then moving to the right column, each entry
is in the format “signal name” followed the three numbers in the order (EXPansion port pin, PROPeller pin, LOGical
Propeller signal name).
Thus, the SD card’s pin 7 is connected thru the HYDRA expansion port’s pin 1 which in turn is connected to the Propeller
chip at pin 21 which is named P16 on the Propeller chips I/O interface. A little confusing, but that’s what happens when
you go from interface to interface to the chip to the final internal Propeller signal name. At the end of the day, as a
programmer all you need to know are the Propeller’s I/O pin assignments which are as follows:
' SPI (serial peripheral interface) interface pins to SD card
spiDO = 16 ‘ SD data out
spiCLK = 1 ‘ SD clock
spiDI = 18 ‘ SD data in
spiCS = 19 ‘ SD card select
‘ these two signals aren’t really part of the SPI interface, but are defined in this block of code
sdWP = 22 ‘ write protect line
sdCD = 23 ‘ card detect line
Next, let’s take a look at the actual mechanical SD card holder used in this project. I selected one from AVX Corporation
based on price, interface, and availability.
Figure 8.0(a) – The HYDRA SD Max SD card connector from AVX Corporation.

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4.2 Mechanical Interface
All SD cards must plug into a physical connector that is mounted to the PCB itself. There are hundreds of manufactures
that make these connectors and selecting one is more subjective than objective in many cases. However, some things
that you should look out for if you decide to design an SD card reader are:
1. Is the connector a normal or reverse type?
2. Does the connector have a spring loaded release? Nice, but expensive.
3. Is the connector plastic or metal or have adequate shielding?
4. Cost, cost, cost! And did I mention cost?
TIP
Normal or reverse connector indicates which way the SD card goes into the connector. Normal
means label facing the front and the contacts facing the PCB. Reverse means the opposite. This is
important depending on which way the PCB is oriented in the final product. In our case, the PCB of
the SD Max card plugs face outward on the HYDRA, so when you plug in the SD card it faces
outward as well.
In the case of the SD Max card we don’t need all the bells and whistles, so we decided on a standard normal connector,
plastic, without a spring eject mechanism (which is probably a good idea since its just one more thing that can break). The
connector itself is manufactured by AVX Corporation and you can find the data sheet on the CD here:
CD_ROM:\docs\datasheets\avx_sd_mech_5638.pdf
Figure 8.0(a) above shows and excerpt from the datasheet illustrating the mechanical specifications of the connector.
Notice that there are a lot of specs and this is one of the biggest challenges when making an SD card reader; designing
the PCB to accept the connector is no easy task due to the small tolerances. Also, notice the additional annotation relating
to the Write Protect and Card Inserted circuits as shown in Figure 8.0(b).
Figure 8.0(b) – Card connector from AVX Corporation showing Write Protect and Card Inserted logic.
These extra signals are available on the SD connector, but not part of the SD specification, thus they aren’t in any specific
location manufacturer to manufacturer. Therefore, when designing SD card PCBs you will find that if you change the SD
card connector, you will have to redesign the PCB footprint quite a bit.

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Figure 9.0 – HYDRA SD Max software / hardware model.
5.0 Interfacing to the HYDRA SD Max Card
In this section we’ll discuss interfacing to the SD card at all levels; electrical to FAT16. Referring to Figure 9.0 above you
can see that the SD card software / hardware model looks a little like the 7-layer OSI model for networking. There is the
application layer at the top. Then under it is the FAT16 file system which facilitates interfacing the SD card with the PC
(optional). Next down is the SD card protocol layer which is what the SD card speaks and gives access to the internal
controller in the SD card as well as raw sector reads and writes. This is followed by the actual communication layer to the
SD card which is a SPI interface consisting of 4-lines; data out, data in, clock, and chip select. Then finally where the
rubber metal the concrete are the electrical connections to the Propeller chip itself that we can toggle via port I/O
commands. Thus, we have to implement every single one of these layers, so we have our work cut out for us!
Our goal is to become familiar with writing a SPI driver all the way up to a DOS/Windows compliant FAT16 file system.
There is a lot of material to cover on the these subjects and each warrants a lot of information, so I suggest referring to
the related links and documents on the CD for more in depth coverage. Take a look in these sub-directories for a number
of relevant documents:
CD_ROM:\DOCS\
\FAT - Documents about the FAT file system.
\SD - Documents about the SD card protocol and design in general.
\SPI - Documents about the SPI interface and protocol.
But, before we begin let’s take an aside briefly and talk about some of the history and design of the SD card protocol.

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Figure 10.0 – SD card physical packaging examples.
5.1 SD Card Overview & History
The SD card was originally invented in 1999 by a collaboration between Panasonic, Toshiba, and SanDisk (lead
developer) to compete with Sony’s Memory Stick technology which was proprietary and a closed standard. The secure
digital aspect of SD card simply has to do with the added functionality supporting encryption that was missing in the MMC
cards beforehand (Multi Media Cards) that the SD card was supposed to replace. Encryption was requested since the
main purpose of the SD card was to hold media data and media providers wanted encryption and some kinds of digital
rights management.
In any event, the SD has become the most popular solid state mass storage device along with Compact Flash storage
devices. Due to this success and the continually shrinking size of consumer electronics new, smaller size, and faster SD
cards are now available. Take a look at Figure 10.0 to see the mini and micro SD card footprints. The mini size is cute,
but the micro is ridiculously small, similar to a cellular phone SIM (Subscriber Identity Module) card. The size of the cards
doesn’t effect the storage capacity. Also, each smaller footprint is designed with the exact same electrical and signal
interface, just smaller and adapters are available to plug each smaller size into each larger size, so even if you have a
normal SD card reader, you can use a micro SD card with a little adapter.
Architecturally, each SD card has a microcontroller inside along with the actual flash memory storage area. Therefore,
when communicating with an SD card you are more or less communicating with another computer. Thus, SD cards are
rather complex pieces of technology that abstract the memory interface and the I/O interface. For example, before SD
cards there were all kinds of memories; RAMs, ROMs, FLASH, EEPROM, etc. but the problem was that if you wanted to
use one of these memories then you had to build a physical interface to them. SD cards removed this problem by
separating the interface from the electronics/memory, so that a user could use a standardized set of communication lines
to talk to a mass storage device. This is the genius of the SD card design. No matter what’s inside the SD card; NAND
flash, NOR flash, holographic memory or little elves, its always the same from the electrical point of view and the
programmers interface. That is, 9 signals that always mean the same thing.
From a programmers point of view the SD card acts like a number of registers and a memory. Communication to the SD
card is done thru a serial/parallel interface by issuing commands and sending and receiving data. The memory in an SD
card is arranged as a number of sectors (512 bytes each usually) and currently SD cards max out at about 4GB of
memory, but 8GB are available. The communication speeds of SD cards depend on the version of the card; 1.0, 1.01, 1.1,
or 2.0. Most manufacturers stick with version 1.1 specs which run at about 10-20 megabytes per second. The speed
measuring of SD cards is based on CD ROM standard. Where 1X CD speed is about 150 kB (kilobytes) per second.
Therefore, an SD card that runs at 66X speed means it runs at 66 x (150 kB) = 9.9MB per second. Currently, 66X and
133X are commonly available with even higher speeds if you’re will to pay the money. However, these speeds are only
attainable in licensed true SD protocol modes, not the free SPI mode (which we are using).
Finally, SD cards are nothing more than a collection of sectors, but to use with PCs, SD cards are setup or “formatted” to
mimic the target file system of the PC they are connected to. Typically, this is FAT16 or FAT32 both Microsoft standards.
Thus, when using an SD on the HYDRA if you want to plug it into the PC you must format in one of these standards.

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Preferably FAT16 since it’s the only format that the drivers support. Of course, you can code FAT32 drivers if you like
yourself.
Summing up, SD cards are memory plus microcontrollers. They are interfaced via a 9-pin electrical interface which is
always the same. Internally, they are organized as a collection of sectors that the programmer can access and read and
write to via issuing commands to the internal microcontroller. If desired, one can layer a file system on top of the raw
sectors like FAT16 or whatever is desired, but you the programmer must do this, SD cards have no built in internal
support for a file system. The actual electrical communication to SD cards is performed via a 1-bit or 4-bit protocol.
However, there is also a standard SPI protocol that can be used which is straightforward to implement. Therefore, the
best place to start talking with SD cards is to build the SPI software and work our way up. In the following sections you will
see SPIN code snippets excerpted from the API library, don’t worry if they don’t make complete sense since we will cover
the API library in detail later in the manual, but for now if you see a global, constant that isn’t defined, trust that it is and
you will learn about it later.
Figure 11.0 – The SPI electrical interface.
5.2 SPI Bus Basics
SPI stands for Serial Peripheral Interface originally developed by Motorola. Its one of two very popular modern serial
standards including I2Cwhich stands for Inter Integrated Circuit by Phillips. SPI unlike I2C (which has no separate
clock) is a clocked synchronous serial protocol that supports full duplex communication. However I2C only takes 2 wires
and a ground. Where SPI needs 3 wires, ground, and potentially chip select lines to enable the slave devices. But, SPI is
much faster, so in many cases speed wins over and the extra clock line is warranted. The advantage of I2C is that you
can potentially hook hundreds of I2C devices on the same 2-bus lines since I2C devices have addresses that they respond
to. SPI bus protocol on the other hand requires that every SPI slave has a chip select line.
Figure 11.0 shows a simple diagram between a master (left) and a slave (right) SPI device and the signals between them
which are:
SCLK - Serial Clock (output from master).
MOSI/SIMO - Master Output, Slave Input (output from master).
MISO/SOMI - Master Input, Slave Output (output from slave).
SS - Slave Select (active low; output from master).
Note: You might find some devices with slightly different naming conventions, but the idea is there is data out and data in,
a clock, and some kind of chip select.
If you refer back to the SD Max interface signals then you will see that the SD card signals have slightly different names.
Assuming the HYDRA is the Master and the SD card is the slave, the mapping of SPI signals are shown in Table 3.0
below:
Table 3.0 – Mapping of SD card signals to official SPI signal names.
SD Card Pin SD Name SPI Signal Name Function
1 CS SS Chip select active low.
2 DI MOSI Master out, slave in.
5 CLK SCLK Clock signal.
7 DO MISO Master in, slave out.
Note: Power and ground signals of course need to be connected as well.

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SPI is very fast since not only is it clocked, but it’s a simultaneous full duplex protocol which means that at you clock data
out of the master into the slave, data is clocked from the slave into the master. This is facilitated by a transmit and receive
bit buffer that constantly re-circulates as shown in Figure 12.0.
Figure 12.0 – Circular SPI buffers.
The use of the circular buffers means that you can send and receive a byte in only 8 clocks rather than clocking out 8-bits
to send, then clocking in 8-bits to receive. Of course, in some cases the data clocked out or in is “dummy” data, meaning
when you write data and you are not expecting a result the data you clock in is garbage and you can throw it away.
Likewise when you do a SPI read, typically you would put a $00 or $FF in the transmit buffer as dummy data since
something has to be sent and it might as well be predictable.
Sending bytes with SPI is similar to the serial RS-232 protocol, you place a bit of information on the transmit line, then
strobe the clock line (of course RS-232 has no clock). As you do this, you also need to read the receive line since data is
being transmitted in both directions. This is simple enough, but SPI protocol has some very specific details attached to it
about when signals should be read and written that is, on the rising or falling edge of the clock as well as the polarity of
the clock signal. This way there is no confusion about edge, level, or phase of the signals. These various modes of
operation are logical called the SPI mode and are listed in Table 4.0 below:
Table 4.0 – SPI clocking modes.
Mode # CPOL (Clock Polarity) CPHA (Clock Phase)
0 0 0
1 0 1
2 1 0
3 1 1
Mode Descriptions
Mode 0 – The clock is active when HIGH. Data is read on the rising edge of the clock. Data is written on the falling
edge of the clock (default mode for most SPI applications).
Mode 1 – The clock is active when HIGH. Data is read on the falling edge of the clock. Data is written on the rising
edge of the clock.
Mode 2 – The clock is active when LOW. Data is read on the rising edge of the clock. Data is written on the falling
edge of the clock.
Mode 3 – The clock is active when LOW. Data is read on the falling edge of the clock. Data is written on the rising
edge of the clock.
Note: Most SPI slaves default to mode 0, so typically this mode is what is used to initiate communications with a SPI
device.

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Figure 13.0(a) – SPI timing diagrams for clock phase polarity (CPHA=0).
Figure 13.0(b) – SPI timing diagrams for clock phase polarity (CPHA=1).
5.2.1 Basic SPI Communications Steps
Figures 13.0(a) and (b) show the complete timing diagrams for all variants of clock polarity (CPOL) and clock phase
(CPHA). You must adhere to these timing constraints during communications. In most cases, you will use mode 0 since
it’s the default that most SPI devices boot with. On the HYDRA there is no support for SPI buses, so we must bit bang the
protocol ourselves by toggling the I/O lines connected to the SPI interface of the SD card. Once again these signals and
Propeller I/O bits are:
spiDO = 16 ‘ SD data out from SD (input to HYDRA)
spiCLK = 1 ‘ SD clock (output from HYDRA)
spiDI = 18 ‘ SD data in (output from HYDRA)
spiCS = 19 ‘ SD card select (output from HYDRA)