8K RAM expansion for the 1541
This modification requires advanced soldering skills. Use it at your
own risk! And, of course, it voids your 1541 warranty (guess you don't have
it anyway, but now you can't say I didn't tell you ;-))
What you need
- 1 4364, 6264 or similar 8x8K SRAM (IC1)
- 1 74LS42 BCD-to-decimal decoder (IC2)
- 2 40-pin DIL precision sockets (highly recommended)
- 1 28-pin DIL socket (recommended)
- 1 16-pin DIL socket (optional)
- A small piece of pre-drilled circuit board (5x7cm)
- A good soldering iron/station
- Some wire. Important: Try to keep the wires as short as possible
(better shorter than on the pictures below!) to maintain reasonable signal
What will the drive look like afterwards?
(Click to see 760x576 images, approx. 128K each)
PCB# 251830, Rev A. With XP1541 cable, 8/9 switch (blue and yellow cable on the left) and 8K RAM expansion board.
There are 26 lines to be connected to UC4 (6502) (8 data bus, 16 address bus,
+5V, 0V). These lines are soldered to the upper 40-pin precision DIL socket's
pins. This socket is then plugged into another socket. It's important to
press them hard together so that each pin has good contact.
(The colored cables in the background have nothing to do with this expansion,
they belong to the XP1541 cable)
RAM expansion board
With 4364 and the 74LS42.
How it works
The additional 8K memory will be mapped at $8000-$9FFF. The stock 1541 mirrors
the $C000-$DFFF ROM here, so the RAM expansion must provide the
*CS (chip select) signal for UB3 (pin 20). Though not really
necessary, it also creates *CS for UB4 ($E000-$FFFF ROM) because
All needed signals (D0-7, A0-15, +5V, GND) are grabbed from UC4
(6502), except R/*W, which is taken from UB2 (2016). IC2
(74LS42) divides the upper 32K address space of the 1541 into four
8K sized blocks:
- there's no extra cost for it
- it cleans up the memory map
- it make the addition of another 8K expansion at $A000-$BFFF very easy
|$8000-$9FFF||IC1, 8K RAM expansion|
|$A000-$BFFF||unmapped (future expansion)|
Using the RAM expansion
I'm not aware of any software except Maverick that makes use of
the additional RAM. However, I hope that there will be a .g64 ripper for
*** schematic bug (2002-06-01) *** (finally fixed 2004-05-20)
The VCC label at UC4, pin 1 (processor socket) is incorrect. A
convenient and correct place to take VCC from is pin 8 of UC4.
8k-expansion.png (31 KB)
8k-expansion.ps.gz (33 KB)
8k-expansion.sch (19 KB). This format is
used by the EAGLE layout editor, Copyright
CadSoft (there's also a freeware-license
for non-profit projects).
me if you have any corrections (can't say I'm an electronics expert ;-)),
suggestions or, most important, software for this piece of silicon.
Thanks in advance.
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Thu May 20 11:18:42 CEST 2004