North Star MDS-A User manual

North star
MICRO-DISK SYSTEM MDS-A
Contents
Parts List . . . . . . . . . . . • 3
Warranty • . . . . . . . . . . . • • . 6
Theory of Operation . . . . . • . 7
Assembly and Check-out . • . . . . . . . . 15
System Integration .......•.. 24
Drawings . . . . . . . . . . . .. .• 27
Copyright 1977, North Star Computers, Inc.

North Star
MICRO-DISK SYSTEM MDS-A
Contents
• • • • • 3
. • • • •. ••. 6
Parts List • • • • •
Warranty • • • • • •
Theory of Operation
Assembly and Check-out
System Integration
Drawings • • • • • • •
• • . . • . . .. 7
. . . • . . . . 15
. . . . .. .. 24
. . • . . . . . • . 27
Copyright 1977, North Star Computers, Inc.

CAUTIONS
1. Correct this document from the errata before doing anything
else.
2. Do NOT insert or remove the MDS controller from the computer
while the power is turned on.
3. Do NOT insert or remove IC's from the board while the power is
turned on.
4. Be sure the +5 volt regulator is generating +5 volt output
voltage before installing any IC·s.
5. Be careful to insert all IC's in correct positions and with
correct orientation.
6. Do NOT connect or disconnect, mount or dismount, or in any way
physically tamper with the disk drive, power board, or disk
controller while the power is turned on.
7. In some cases disk drives may not operate properly if located
in the vacinity of TV's, electric motors, or other sources of
electrical noise. This may be remedied by moving the disk
drive away from the noise source or by installing the disk
drive in a grounded cabinet.
North Star MICRO-DISK System
2

PARTS LIST
MDS SYSTEM PARTS
disk ~rive, Shugart SA-400
ribbon cable assembly
diskette, blank
1
1
1
1
1
1
1
1
1
1
diskette, pre-recorded with software
MDS manual
DOS manual
BASIC manual
OEM manual
MDS controller with parts
power board with parts
MDS CONTROLLER PARTS
1 printed cirCuit board (5" x 10")
1 bo1t,6-32x1/2"
1 lock washer
1 nut, 6-32
1 heat sink, 61018-14
1 5 volt regulator, 7805 or 340T-5
1 crystal, 4MHz
23 16-pin low profile IC sockets
24 14-pin low profile IC sockets
1 34-pin cable connector header
Integrated Circuits
3 74LS00 1
1
74LS02
1
2
74LS08
7
1
74LS11
1
4 74LS14
1·
1 74LS30
2
2
74LS32 1
1
74LS42 2
5
74LS74
1
4
74LS109 2
1 74LS132
3
74LS157
74LSi60
74LS161
74LS164
74LS174
74LS257
7404
74.38
74166
74367
6301-1
3 North Star MICRO-DISK System
or 74S287

Capacitors
1
1
1
1
18
Resistors
2
.4
2
100uf electrolytic
6.8uf tantalum
470pf dipped mica
33pf dipped mica
.047uf ceramic disc
680 ohm
150 ohm
2.2 K
Cl
C2
C3
C4
by-pass
Rl,R2
R3 , R4 , R5 ,R6
R7,R8
MDS POWER BOARD PARTS
1
1
1
2
1
1
1
1
3
3
3
1
4
1
1
2
2
printed circuit board, 3" x 51/2"
1% resistor, RN55D 232 ohm
1% resistor, RN55D 1 .. 96 K
capacitors, .047uf ceramic disc
regulator, 7805 or 340T-5
regulator, LM317K
heat sink, 295-2
heat sink, 690-3-B
bolts, 6-32xl/2"
lock washers
nuts, 6-32
power plug
power plug pins
4 conductor power cable, 5 feet
strain relief bushing
bolts, ~-32xl 1/4"
spacers
North Star MICRO-DISK System
4

POWER SUPPLY PARTS (MDS-PS option)
I
I
I
I
I
I
I
I
2
2
2
2
2
I
115v cord set, 8 feet
strain relief bushing
fuse holder
fuse, IA 3AG
toggle switch
transformer
capacitor, 3000uf30wvdc electrolytic
capacitor, 2500uf 15wvdc electrolytic
rectifier diodes, MR501 3A
rectifier diodes, IN4002 IA
bolts, 6-32xl/2"
lock washers
nuts, 6-32
hook-up wire
CABINET PARTS (MDS-CAB option)
I
I
4
4
6
5
cabinet base plate
cabinet cover
stick-on rubber feet
6-32 flat head screws
6-32 pan head screws
North star MICRO-DISK System

WARRANTY
North Star Computers, Inc. warrants the electrical and mechanical
parts and workmanship of this product to be free of defects for a
period of:
a) 90 days from date of purchase, if purchased in kit form, or,
b) 180 days from date of purchase, if purchased assembled.
If such defects occur, North Star Computers, Inc. will repair the
defect at no cost to the purchaser. This warranty does not
extend ~ defects resulting from improper use or assembly by
purchaser, nor does it cover transportation to the factory.
Also, the warranty is invalid if all instructions included in the
accompanying documentation are not carefully followed. Should a
unit returned for warranty repair be deemed by North Star
Computers, Inc. to be defective due to purchaser's action, then a
repair charge not to exceed $30 without purchaser's consent will
be assessed. Any unit or part returned for warranty repair must
be accompanied by a copy of the original sales receipt. This
warranty is made in lieu of all other warranties, expressed or
implied, and is limited to the repair or replacement of the
product.
North Star MICRO-DISK System 6

THEORY OF OPERATION
The North Star MICRO-DISK System (MDS) controller is an .
integrated system of hardware and software. It is designed
specifically to provide a complete, compact and economic~l disk
drive controller for use with S-100 bus 8080 or Z80microcomputer
systems •.
HARDWARE
The MDS controller is implemented entirely from medium and
small scale TTL integrated circuits and PROM memory. The entire
controller fits on. a single 51 x10" printed circuit card. The
following diagram sh6ws the general organization of the MDS
controller.
1. Addr ess Buffe r sand Selec t Log ic • 'l'he six teen ,add ress 1 ines
are buffered with Schmidt trigger inverters (4G, 5G, 6G) to
provide additional noise immunity. The high order 8 address
lines are used by the board select PROM (7G) to determine if
the current memory reference is addressing the controller
board. The low order eight address lines are used to present
data and commands to the controller. The use of these bits is
determined by the outputs of the board select PROM.
2. write Data Logic. If the controller is issued a write data
byte command, then the low orde~ eight address bits are
interpreted as data to write and are gated into the write
shift register (3G). The controller will place the CPU in a
wait state unt.il the shift register is empty and only then
clock the new data into the shift register. The output of the
shift register is combined with clock pulses and encoded
(using FM encoding method) for output to the disk drives.
3. Read Data Logic. Raw data from the disk (READ DATAl) is
buffered with a Schmidt trigger and formed into one clock
period pulses (NICE READ DATA) ,synchronous with the controller
clock(LCLK/). 'l'he clock and data pulses are separated by the
data separation logic (2A and associated gates) and the
resulting data bit is saved in a flip-flop, and then it is
clocked into the 8 bit shift register(5E). The read shift
register outputs are multiplexed with the status bits (2F, 4F,
4E) and driven onto the Data Input Bus (SF, 6F).
7
North Star MICRO-DISK System

8 DI Bus
Address
Bus
16
256/512
Byte MPXR
ROM
8
8
Status
Bits
8 8-bit
shift reg
Board Select Data
, Control Lo~ic Encoder
Controls
to
Disk
Controls
from
Disk
Data'
to
Disk
MDS Controller Block Diagram
North Star MICRO-DISK System
(to 8(80)
8
8;"bit
shift reg
Data
Separator
Data
from
Disk
8

4. On Board PRONe Controller software (8080 or Z80 machine code)
is stored, in part, in two on-board 4x256 bit bipolar PROMs.
These PROMs provide 256 bytes of memory. Replacihg these
PROMs with pin compatible 4x512 PROMs would provide 512 bytes
of on-board program. The 8 low order address bits address the
PROMs. The. PROM outputs are driven onto the Data Input Bu~.
5. Clock Circuit. The crystal. controlled clock circuit (SA, 58,
4A, 6A) provides 2 MHz clock signals to synchronize all the
control circuitry.
6. Read, Write Control. A read or write command sequence begins
with detection of a sector pulse. A read or write command
must be issued to the controller within a 96 microsecond
window after the sector pulse. Writing data begins at the end
of the window •. The controller writes one byte of zeros.
Fifteen additional bytes of zeros are written by the software
commands followed by a synchronization character, 256 bytes of
data, and a cyclic check character. writing stops at the next
sector pulse. Reading starts some time afte~the end of the
window so as to be in the middle of the wr i't ten zeros. A read
sequence starts in "hunt" mode. When a sync character is
detected, the controller enters "body" mode. Whehthe
software issues a read command to the controller, the
controller will put the CPU into the wait state until the read
shift register is full. The read loop must complete in less
than 64 microseconds.
7. Command Decode Logic. When a .command address is issued to the
controller, the 8 low order address bits are decoded to
determine which command actions are to be taken and which disk
cQntrols should be performed. See the COMMANDS section for
details.
8. Counters. The counters ID, 2D, IE, and 2E provide the timing
for write data shifting, data encoding and counting, and read
and write command sequencing. The counter IG is the sector
position counter. The outputs of 2E provide ps~udo sector
pulses in case no diskette is inserted in the drive or the
drive motor is off and also allow discrimination between
9
. .
sector holes and the index hole. The counter IF is used to
count disk revolutions to determine when to cause automatic
motor off. The counter 28 is used to count bits while reading
data.
North Star MIC'RO-DISK System