mirror of
https://github.com/hsoft/collapseos.git
synced 2024-11-15 20:58:06 +11:00
62 lines
2.5 KiB
Plaintext
62 lines
2.5 KiB
Plaintext
# Writing to a AT28 from Collapse OS
|
|
|
|
# Gathering parts
|
|
|
|
* A RC2014 Classic
|
|
* An extra AT28C64B
|
|
* 1x 40106 inverter gates
|
|
* Proto board, RC2014 header pins, wires, IC sockets, etc.
|
|
|
|
# Building the EEPROM holder
|
|
|
|
The AT28 is SRAM compatible so you could use a RAM module for
|
|
it. However, there is only one RAM module with the Classic
|
|
version of the RC2014 and we need it to run Collapse OS.
|
|
|
|
You could probably use the 64K RAM module for this purpose, but
|
|
I don't have one and I haven't tried it. For this recipe, I
|
|
built my own module which is the same as the regular ROM module
|
|
but with WR wired and geared for address range 0x2000-0x3fff.
|
|
|
|
If you're tempted by the idea of hacking your existing RC2014
|
|
ROM module by wiring WR and write directly to the range
|
|
0x0000-0x1fff while running it, be aware that it's not that
|
|
easy. I was also tempted by this idea, tried it, but on bootup,
|
|
it seems that some random WR triggers happen and it corrupts the
|
|
EEPROM contents. Theoretically, we could go around that by
|
|
putting the AT28 in write protection mode, but I preferred
|
|
building my own module.
|
|
|
|
I don't think you need a schematic. It's really simple.
|
|
|
|
# Writing contents to the AT28
|
|
|
|
If you wait 10ms between each byte you write, you can write dir-
|
|
ectly to the AT28 with regular memory access words. If you don't
|
|
wait, the AT28 writing program will fail. Because it's not very
|
|
pratical to insert waiting time between each byte writes, you
|
|
need another solution.
|
|
|
|
To that end, Collapse OS has a "memory write override" mech-
|
|
anism. Whenever C! or ! is about to set a byte somewhere in
|
|
memory, it checks whether such an override is active. If it is,
|
|
it calls it. That override is set with the "~C!" word.
|
|
|
|
B400 contains an override routine compatible with ~C! called
|
|
~AT28. When you're about to write to your AT28, activate that
|
|
override with "' ~AT28 ~C!". That overwrite will write the byte,
|
|
then poll the AT28 until it indicates that it is finished
|
|
writing. This ensures that Collapse OS doesn't try writing
|
|
another byte before the AT28 is ready.
|
|
|
|
When you're done writing to the AT28, unset override with
|
|
"0 ~C!". The override routine has a non-negligible speed impact
|
|
on all memory writes.
|
|
|
|
When polling, ~AT28 also verifies that the final byte in memory
|
|
is the same as the byte written. If it's not, it will place a
|
|
non-zero value in the ~C!ERR 1b variable. Therefore, if you want
|
|
to see, after a big write operation to your AT28, whether any
|
|
write failed, do "~C!ERR C@ .". Re-initialize to zero before
|
|
your next write operation.
|