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v20prom.txt
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2007-09-10
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95 lines
----------------------------------------------------------------------------
Copyright (c) Carl W. Houseman, 1985. All rights reserved.
----------------------------------------------------------------------------
Restoring Auto- and Floppy- Boot
with the NEC V20 Processor
--------------------------------
An easy way to get some additional computing power out of your Rainbow is
to install an NEC V20 (uPD70108) microprocessor in place of Intel's 8088
processor. Unfortunately, the Rainbow firmware is not prepared for the
faster V20, and self test fails. The result is that 100B/100+ systems will
not auto-boot (the Winchester can still be booted manually), and boot from
floppy is impossible in all models.
You can restore the auto-boot and floppy boot capability to your system by
making a modified copy of the rom containing the self-test and boot firmware.
NOTE, HOWEVER, THAT DEC's COPYRIGHT NOTICE PREVENTS YOU FROM MAKING COPIES
FOR ANYONE BUT YOURSELF.
The rom modificatons should work for versions 04.03.11A of the 100A, and
05.03A of 100B/100+ boot firmware (the first number before the "." identifies
the boot rom). However, subtle differences may exist in the boot rom without
an external version number change, so before removing the rom, check for the
correct version as follows:
1. Start DEBUG at the MS-DOS prompt
2. Enter one of the following DEBUG commands, depending on your system:
100A: 100B/100+:
D FA00:1FFE 1FFF D F400:3FFE 3FFF
3. You should see:
FA00:1FF0 91 B2 F400:3FF0 47 A0
(extra spaces in the display and trailing characters not shown here)
If you have the correct version, you'll need a blank 2764 (100A) or 27128
(100B/100+) eprom for the copy, plus access to the following equipment:
o A prom programmer/duplicator which allows specific prom locations
to be changed for a duplicate operation
o A small flat blade screwdriver
o A chip extractor (preferred to a screwdriver for 100B/100+)
o The Pocket Service Guide (EK-PC100-PS-002) or Technical Manual
Addendum (EK-RB100-TM-001)
Disassemble the system and remove the boot rom, being very careful with the
socket in 100A systems as noted in the technical documentation. Set up the
prom programmer to program the locations with data as indicated (all
hexadecimal):
100A: 100B/100+:
Location Data Location Data
043F 64 072F 64
067D 20 0B36 20
1FFE 2B 3FFE 1B
1FFF 70 3FFF 88
When you replace the 8088 with a V20, replace the boot rom at the same time.
The modified rom will not work with the 8088 installed.
I'd like to hear from anyone who succesfully modifies a 100A prom, since only
the 100B version has been tested. If your boot rom fails the version check,
give me a call to discuss the details of making the changes to a different
rom version.
Carl Houseman
703-337-4565 (evenings)
-----------------------------------------------------------------------------
Comments on the text by Tom, 4-SEP-1993:
This file was sent to me by Nigel W. Johnson and I now contribute it to
the ftp area of ftp.update.uu.se. Nigel confirmed that the patch also
works with a 100A model.
If you have problems locating the right EPROM and doesn't have a manual
describing which EPROM to modify, you can always mark them all (to be sure
that you insert them correctly later in their proper places) and pull them
all out. Then use the EPROM reader/burner to read the two last positions in
each EPROM. The right one should say '91 B2' for a 100A and '47 A0' for
a 100B/+. On 100B models (I only have B models), the right PROM is the one
closest to the front of the machine (of the two PROMs located near the
8088 cpu).
(tomk@update.uu.se)