
Originally Posted by
Chuck(G)
It doesn't really matter to me--they program the same way. I think I can get most of the pins to line up--let me play around a bit. At least most of the address lines are on the left side and the data output lines are on the right side of the 82S23, so it's not beyond hope that we'll get at least most of them to line up.
Actually only 3 of the 4 data lines are used, and each configuration is only 16 words, so a 16x3bit memory would be enough to store a single desired configuration. However, then switches 3/4 and jumper E2 won't do anything.
Two of the data lines will select the bank number, and the third data line just enables the bank sellected. Here is a thruth table:
Code:
D3
|D2
||D1
|||D0
||||
vvvv
xxx0 = Segment not mapped to any RAM bank
x001 = Segment mapped to RAM bank 0
x011 = Segment mapped to RAM bank 1
x101 = Segment mapped to RAM bank 2
x111 = Segment mapped to RAM bank 3
The segment number is presented directly on A0-A3 of U44, where the rest of the Ax lines are connected to switches 3/4 and jumper E2 (as a way to select between up to 16 different configurations).
Current systems owned by me:
Vintage:IBM PC/XT submodel 087 ( 1983 ), [Kon]tiki-100 rev. C (1983), Compaq Portable I ( 1984 ), IBM PC/XT submodel 078 ( 1985 ), IBM PC/XT286 ( ~1986 ), 3x Nintendo Entertainement Systems ( 1987 ).
Obsolete:Commodore A500 ( ~1990 ), IBM PS/2 model 70/386 type 8570-161 ( 1991 ), Atari Lynx II ( ~1992 ), Generic Intel 486SX PC ( ~1993 ), AT/T Globalyst Pentium w/FDIV bug MB ( 1994 ), Compaq 486DX4 laptop ( ~1995 ).
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