29 Aug
2002
29 Aug
'02
8:29 a.m.
Yes, these are the switches in the upper left. But
knowing that they
are address selection switches does not help much. I presumed they
were. But there appear to be 4 banks of 4K RAM. That should only
require about 4 switches for selection. There are 16 switches
however.
Each 4k page has 4 switches, numbered A12 to A15, and there
are 4 pages. The four switches determine the starting address,
between 0000 and F000, of that page. Page 1 = upper left switches,
page 2 = upper right, page 3 = lower left, page 4 = lower right.
So, if you have the manual, can you say what the
specific switch
assignements are?
Starting address DIP switch setting
Decimal Hex A15 A14 A13 A12
0 0000 x x x x
4,096 1000 x x x c
8,192 2000 x x c x
12,288 3000 x x c c
16,384 4000 x c x x
20,480 5000 x c x c
24,576 6000 x c c x
28,672 7000 x c c c
32,768 8000 c x x x
36,864 9000 c x x c
40,960 A000 c x c x
45,056 B000 c x c c
49,152 C000 c c x x
53,248 D000 c c x c
57,344 E000 c c c x
61,440 F000 c c c c
x= switch open, off, or down position
c= switch closed, on, in up position
Also, what is the analog circuitry in the lower right,
with the delay
module?
According to the manual, the lower section of the board is
all the control logic and U70, which is down along the lower edge in
the right corner, is for the protect/unprotect logic. U71 is a delay
line. Verbatim from the manual it states:
"MC and RC are or'ed in U61, with the output on pin 8 being
applied to U71. U71 is a delay line with outputs which reproduce MC+
RC delayed by 100 nsec (pin 14), 150 nsec (pin 4), 250 nsec (pin 12)
and 350 nsec (pin 6). This is a passive delay line consisting of LC
sections and TTL drivers built into the input and output lines".
I hope this helps. Unfortunately this is one of the
Processor Tech manuals that doesn't seem to be in PDF format on Bob
Stek's site.
Jeff
--
Home of the TRS-80 Model 2000 FAQ File
http://www.cchaven.com
http://www.geocities.com/siliconvalley/lakes/6757