Rainbows and NEC V20 upgrades.

From: Mark Tapley <mtapley_at_swri.edu>
Date: Sat Apr 20 18:39:18 2002

Rainbow owners,
        I did get a request for the mods to make a Rainbow run with an NEC
V20. Info below is from a reprint from the Rainbow News; unfortunately I
don't have the date or the original issue, only the reprint. The article
does carry the notation, Copyright (c) 1986 by Carl Houseman, all rights
reserved, which means I'm probably about to get myself into potential legal
trouble here. Carl, contact me if you are listening, I'll try to work out
something you are happy with.
        Paraphrased heavily, the reprint says there is a 5% speed
improvement overall, with up to 33% improvement (max.) for routines using
the "fast video" firmware options. GW-Basic has a problem with displaying
characters in the medium resolution graphics screen, and a hard disk
diagnostic (test #4, seek time) doesn't work.
        There is also a set of problems with booting, but these are
supposed to be fixed by the below modifications to the boot EPROM (though
the article includes the expected YMMV-and-your-machine-may-explode kind of
disclaimers). The EPROM is, for a Rainbow 100B or 100+, a 27128 PROM. If
you install a V20, that EPROM (located between the connectors for the hard
disk option) should be duplicated with the following changes:

Location Data
-------- ----
072F 64
08E6 E8
08E7 17
08E8 36
08E9 90
0B36 20
3F00 51
3F01 B9
3F02 04
3F03 00
3F04 D4
3F05 0A
3F06 E2
3F07 FC
3F08 59
3F09 C3
3FFE EC
3FFF B2

For a PC100A, the Hard disk problem is irrelevant, the EPROM is a 2764, and
the change list is:

Location Data
-------- ----
043F 64
067D 20
1FFE 2B
1FFF 70

Let me know if you try it; I have not. Good luck!
                                                        - Mark
Received on Sat Apr 20 2002 - 18:39:18 BST