2020-10-30 20:31:47 -04:00
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# Writing to a AT28 from Collapse OS
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# Gathering parts
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* A RC2014 Classic
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* An extra AT28C64B
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* 1x 40106 inverter gates
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* Proto board, RC2014 header pins, wires, IC sockets, etc.
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# Building the EEPROM holder
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The AT28 is SRAM compatible so you could use a RAM module for
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it. However, there is only one RAM module with the Classic
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version of the RC2014 and we need it to run Collapse OS.
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You could probably use the 64K RAM module for this purpose, but
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I don't have one and I haven't tried it. For this recipe, I
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built my own module which is the same as the regular ROM module
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but with WR wired and geared for address range 0x2000-0x3fff.
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If you're tempted by the idea of hacking your existing RC2014
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ROM module by wiring WR and write directly to the range
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0x0000-0x1fff while running it, be aware that it's not that
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easy. I was also tempted by this idea, tried it, but on bootup,
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it seems that some random WR triggers happen and it corrupts the
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EEPROM contents. Theoretically, we could go around that by
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putting the AT28 in write protection mode, but I preferred
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building my own module.
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I don't think you need a schematic. It's really simple.
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# Writing contents to the AT28
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Rename A!, A@ and A, to C!*, C@* and C,*
Also, rename "Addressed devices" to "Indirect memory access".
I do this because I need to add indirect versions of !, @ and ,
to allow boostrapping directly to EEPROM and that A,, thing I've
added to assemblers felt like really bad names.
With this change, I'd like to generalize the use of the * suffix
for aliases.
2020-12-07 19:06:58 -05:00
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There is an AT28! writer word in B400 which is C!*-compatible
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(see "Indirect memory access" in doc/usage.txt) and and waits
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until the write is complete before returning. If you use C!
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directly, bytes you write might not have the time to completely
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write themselves before you write another one.
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To use, set C!* with "' AT28! ' C!* **!". Once this is done, you
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can use MOVE, or /tools/upload, both will call C!* and do the
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right thing. Unset C!* with "' C! ' C!* **!" afterwards.
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B400 also has AT28, which is the same as AT28!, but for C,.
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