IBM 5-1/4" Diskette Drive Adapter Application guide

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Personal Computer
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Hardware Reference
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Library
mM 5-1/4" Diskette
Drive Adapter
6361505

ii

Contents
Description .................................... 1
Programming Considerations
...................... 3
Digital-Output Register
...................... 3
Floppy Disk Controller
....................... 4
Command Summary
......................... 8
Programming Summary
...................... 17
Interface ..................................... 19
System
I/O Channel Interface ................ 19
Drive A and B Interface
..................... 20
Specifications
................................. 23
Logic Diagrams
................................ 25
Hi

iv

Description
The IBM 5-1/4" Diskette Drive Adapter fits into one of the
expansion slots in the system unit.
It is connected to one or two
diskette drives through an internal, daisy-chained flat cable. The
adapter has a connector
at the other end that extends through the
rear panel of the system unit. This connector has signals for two
additional external diskette drives; thus, the
5-1/4 inch diskette
drive adapter can attach four
5-1/4 inch drives -two internal
and two external.
The adapter
is designed for double-density, MFM-coded, diskette
drives and uses write precompensation with an analog phase-lock
loop for clock and
data recovery. The adapter is a
general-purpose device using the
NEe fLPD765 or equivalent
controller. Therefore, the diskette drive parameters are
programmable. In addition, the attachment supports the diskette
drive's write-protect feature. The adapter
is buffered on the I/O
bus and uses the system board's direct memory access (DMA) for
record data transfers.
An interrupt level also is used to indicate
when an operation
is complete and that a status condition requires
microprocessor attention.
In general, the
5-1/4 inch diskette drive adapter presents a
high-level command interface to software
I/O drivers.
Diskette Adapter 1

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Direction
Disk
8
Controller
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Enable
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Head
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Write
Protect
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Track
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Drive
A
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VI
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Digital
-
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Drive
A
Select
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5-1/4Inch Diskette Drive Adapter Block Diagram
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Programming Considerations
This attachment consists of an 8-bit digital output register in
parallel with a
NEC JLPD765 or equivalent floppy disk controller
~ (FDC).
In the following description, drive numbers 0, 1, 2, and 3 are
equivalent to drives A, B, C, and D.
Digital-Output Register OJ / ..
The Digital-Output register (DOR) is an output-only register used
to control drive motors, drive selection, and feature enable. All
bits are cleared
by the II 0 interface 'reset' line. The bits have the
following functions:
Bits 0 and 1 These bits are decoded
by the hardware to
select one drive if its motor
is on:
Bit 1 0 Drive
00
o (A)
01
1 (B)
10
2 (C)
1 1 3
(D)
Bit 2 The
FDC is held reset when this bit is clear.
It must be set by the program to enable the
FDC.
Bit 3 This bit allows the
FDC interrupt and DMA
requests to be gated onto the I/O interface.
If this bit is cleared, the interrupt and DMA
request I/O interface drivers are disabled.
Bits
4,5,6,
These bits control, respectively, the motors of
and 7 drives 0,
1,2 (A, B, C), and 3 (D). If a bit is
clear, the associated motor is off, and the
drive cannot be selected.
Diskette Adapter 3

Floppy Disk Controller
The floppy disk controller (FDC) contains two registers that may
be accessed
by the system unit's microprocessor: a status register
and a data register. The 8-bit main status register contains the
status information
of the FDC and may be accessed at any time.
The 8-bit data register (actually consisting of several registers in a
stack with only one register presented
to the data bus at a time)
stores data, commands, parameters,
and provides floppy disk
drive
(FDD) status information. Data bytes are read from or
written to the data register in order to program or obtain results
after a particular command. The main status register can only be
read and is used to facilitate the transfer of data between the
system unit's microprocessor
and FDC.
The bits in the main status register (hex 34F) are defined as
follows:
Bit
Number
Name Symbol
Description
DBO
FDD A Busy
DAB FDD number 0 is in the Seek mode.
DB1
FDD B Busy DBB FDD
number 1 is in the Seek mode.
DB2 FDD C Busy DCB FDD
number 2 is in the Seek mode.
DB3 FDD D Busy DDB FDD
number 3 is in the Seek mode.
DB4 FDC Busy CB A read or
write command is in process.
DB5 Non-DMA
NDM
The FDC is in the non-DMA mode.
Mode
DB6 Data Inputl
DIO
Indicates direction of data transfer
Output
between FDC and processor. If DIO = "1;'
then transfer is from FDC data register to
the processor. If DIO = "0;' then transfer
is from the processor to FDC data register.
DB7 Request
for
ROM Indicates data register is ready to send or
Master
receive data to or from the processor. Both
bits DIO and ROM should be used to
perform the handshaking functions of
"ready" and "direction" to the processor.
The FOe is capable of performing 15 different commands. Each
command is initiated by a multi-byte transfer from the system
unit's microprocessor,
and the result after execution of the
command may also be a multi-byte transfer back to the system
4 Diskette Adapter

unit's microprocessor. Because of this multi-byte interchange of
information between the
FDC and the system unit's
microprocessor, it
is convenient to consider each command as
consisting of three phases:
,~ Command Phase
The FDC receives all information required to perform a particular
operation from the system unit's microprocessor,
Execution Phase
The FDC performs the operation it was instructed to do.
Result Phase
After completion of the operation, status and other housekeeping
information are made available to the system unit's
microprocessor,
The following tables define the symbols used in the command
summary. The command summary immediately follows these
tables,
Diskette Adapter 5

Symbol
Name
AO
Address Line 0
C
Cylinder Number
D Data
D7-DO Data Bus
DTL Data Length
EDT End
of Track
GPL Gap
Length
H Head
Address
HD Head
HLT Head Load
Time
HUT
Head Unload Time
MF FM or MFM Mode
MT
Multi-Track
N Number
Description
AO
controls selection of main status
register (AO = 0) or data register (AO =1 ).
C stands for the current/selected cylinder
(track) number of the medium.
D
stands for the data pattern that is going
to be written into a sector.
8-bit data bus, where D7 stands for a
most significant bit, and DO stands for a
least significant bit.
When N is defined as 00, DTL stands for
the data length that users are going to
read from or write to the sector.
EDT stands for the final sector number on
a cylinder.
GPL
stands for the length of gap 3
(spacing
between sectors excluding VCO
sync field).
H
stands for head number 0 or 1, as
specified in
ID field.
HD
stands for a selected head number 0
or 1. (H =HD in all command words).
HLT stands for the head load time in the
FDD (4 to 512 ms in 4·ms increments).
HUT stands for the head unload time after
a read or write operation has occurred (0
to 480 ms in 32-ms increments).
If MF is low, FM mode is selected; ifit is
high,
MFM mode is selected only if MFM
is implemented.
If MT is high, a multi-track operation is to
be performed. (A cylinder under both HDO
and HD1
will be read or written.)
N stands for the number of data bytes
written in a sector.
Symbol Descriptions (Part 1 of 2)
6 Diskette Adapter