Notes On Various Micro Decision Models
Chassis Versions
There were three chassis types used in
Micro Decisions: A, B and C.
The Revision A chassis is generally
the type found for early MD2 models with Rev 1.1 motherboards. This
chassis is identifiable by a cord
pan in the rear of the
unit. The standard power supply on these
chassis had a hard-wired AC
power cord.
The Revision B chassis is generally
the type found for later MD2 models with Rev 2.0 motherboards. This
chassis has, instead of a cord
pan, a grille across the
upper-back of the unit for ventilation. The
power cord is not hardwired and
plugs into the back of the powersupply.
The Revision C chassis has a knockout
to accomodate a ventilation fan,
and drive-expansion knockout on the rear right-hand side (when viewed from the back of the unit), and a
removable tray which mounts the
motherboard for removal from the back of the unit. The power cord
is not hardwired and plugs into
the back of the power supply.
Motherboard Versions
There are two Micro Decision
motherboard revisions: Rev 1.1 and
Rev 2.0.
The Rev 1.1 boards were phased out May
27, 1983 and are generally
found in Revision A chassis. These motherboards support two serial ports, switch-selectable baud rates, and a
34-pin edge connector or
external floppy expansion. These motherboards can only employ a 2-kilobyte 2716-type PROM.
Rev 2.0 boards came in two versions:
Japan (Kohjinsha) and Korea.
These boards are generally found in Revision B and Revision C chassis. These motherboards support
two serial ports, software-
selectable baud rates, a Centronics compatible parallel port, a 34-pin I/O edge-connector for "future
enhancements" (no longer used
for floppy expansion), jumper-able motherboard diagnostics accessible via the ROM, and an improved floppy-disk
data separator. These
motherboards employ a 4-kilobyte 2732-type PROM, but can utilize a 2-kilobyte 2716-type PROM with a
motherboard jumper cut.
The Rev 2.0 motherboard will not run
CP/M with a Morrow revision lower
than 2.1. The Rev 1.0 motherboard will not run CP/M with a
Morrow
revision greater than 1.6.
Floppy drives are connected as follows:
Both Rev 1.0 and 2.0 motherboards
attach Drive A to the left-most
internal 34-pin edge connector and Drive B to the right-most connector.
Rev 1.0 motherboards Drives C and D
can be either daisy-chained from
the Drive B connector, or from the rear floppy expansion connector.
Rev 2.0 motherboards drives C and D
are daisy-chained from the Drive B connector.
ROM Versions
ROM
Motherboard
CP/M Source
Version
Version 2.2 Ver
Size Avail? Notes
------- --------------- -------
------- -------
------------------------------
1.3
1.1
1.3 min 2k Yes
The only MD2 version I've come
across. (1)
2.0
2.0
2.0 min 4k
No (1)
2.3
2.0
2.0 min 4k
No (1)
2.5
2.0
2.0 min 4k
No (1)
3.1
2.0
3.0 min 4k Yes
Floppy error handling fixups.
SELDSK, console output and
translation moved into ROM.
(1) A ROM software bug
with the motor control bits
prevents a 4th floppy from
being accessible.
CP/M to ROM Compatibility
CP/M
2.2
Version
|
Machine
|
Minimum
ROM Version
|
1.x
|
MD2
Rev 1
|
1.3
|
2.1
|
MD2
Rev 2/MD3
|
2.0
|
2.5
|
MD2
Rev 2/MD3
|
3.1
|
Boot Disk Version
Compatibility
CBIOS
Version
|
Format
|
Machine
|
CP/M 2.2 Rev 1.3
|
SSDD
|
MD2 Rev 1
|
CP/M 2.2 Rev 1.3
|
DSDD
|
MD2 Rev 1
|
CP/M 2.2 Rev 1.5
|
SSDD
|
MD2 Rev 1
|
CP/M 2.2 Rev 1.5
|
DSDD
|
MD2 Rev 1
|
CP/M 2.2 Rev 1.6
|
SSDD
|
MD2 Rev 1
|
CP/M 2.2 Rev 2.1
|
DSDD
|
MD2 Rev 2/MD3
|
CP/M 2.2 Rev 2.5
|
DSDD
|
MD2 Rev 2/MD3
|
MD2 Rev. 1 Power Supplies
I have encountered two types of power
supplies on Micro Decisions.
The first type has the power cord
built-in to the power supply unit. Care should be taken with these when
adding additional floppies.
If a third floppy drive is
added, this unit can easily be blown.
The second type has a standard
removable power cord common to most computing equipment. This is a
higher-rated power supply, however the actual rating is unknown. These
types of power supplies have
presented no difficulty handling four 5.25-inch floppies.
The MD2 and MD2 motherboards require
+5/+12/-12 voltages.