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64KNCN.ARK
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2006-10-19
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The FAST RAM upgrade I did to my 4A gives about a 50% increse in speed and puts
A full 64K of ram in the console. Of course, only 32K is usable without some
more modification. Some Of the possable modifications are: ram at >6000->8000
when no ram is in the cartridge, bank switch out the ROMs in the console, have
ram at >4000->6000 when not using a DSR, ram from >8000-8400, (so far that is
ram from >0000 to >8400 and ram from >A000 to >FFFF 24K+33K=57K), and with a
lot of decoding most of the other area could be filled in. I think it would be
easer to put the >8000->A000 over the ROMs making two banks of ram there.
As of now I only have the normal 32K of ram active. But when I get back into
it I will build up a board to hold all the decoding and bank switching hardwear
The parts I have used so far are:
2-64LS128 RAm chips at about $16.00 each= $32.00
1-74LS21 four input AND gate 1.50 1.50
1-74LS153 dual 4-input multiplexer $2.00 2.00
About 3 feet of wire 1.50
TOTAL PARTS $37.00
CONSTRUCTION DIRECTIONS: Do at your own risk
Remember TI numbers some of their chips funny.
Bend out all pins on the ram chips that cannot be made to line up with the Roms
(U610 and U611) and the CE pin on the rams (all but about 10 or so pins can be
made to line-up).
Solder the ram chips over the rom chips and wire the rest of the pins on the
rams to the correct outputs of the micro (TMS9900-U600) except the CE and OE
Ground the OE pin.
USED FOR DECODING
Solder the 74LS21 over U504 (74LS138) connecting inputs to pins Y1,Y5,Y6 and Y7
Connect the output from one half to an input for the other half. Tie all
unused inputs HIGH.
USED TO ELIMINATE SOME WAIT STATES.
Solder the 74LS153 to any convenent place around the micro. Hook the output
of the 74LS21 to "S0" of the 74LS153. Ground the "E" line. Cut the trace
from U606-pin 11 to U605 pin 13. Connect pin 11 to "S1" and connect pin 13 to
"Za" of the 74LS153. Tie "Input 3A" high. The rest of the "A" inputs LOW.
Solder the output of the 74LS21 also to the CE pins of the ram chips.
NOTES::
common pins are by function and location NOT location and NUMBER
!!!!ASK ALL QUESTIONS BEFORE YOU START!!!!
E-MAIL to MIKE-AB will be answered when I read it. Questions in the RT may
not be answered the same day I read them. All answers will be in RT.
MIKE-AB [MIKE-B]
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