27 lines
1.1 KiB
Plaintext
27 lines
1.1 KiB
Plaintext
|
# Writing to a AT28 from a SMS
|
||
|
|
|
||
|
|
Writing on the EEPROM that is currently running Collapse OS is
|
||
|
|
as easy as enabling the WE pin on your hacked up cartridge. How-
|
||
|
|
ever, this is not practical: If you want to deploy Collapse OS
|
||
|
|
(or something else) to another machine, or even if you want to
|
||
|
|
upgrade your current Collapse OS, you will likely want to write
|
||
|
|
to another EEPROM.
|
||
|
|
|
||
|
|
The easiest way to do so is to build yourself a dual EEPROM
|
||
|
|
cartridge. It's very similar to a simple cartridge, except it
|
||
|
|
has two AT28 sockets and a '139 decoder to select between the
|
||
|
|
two.
|
||
|
|
|
||
|
|
The design proposed here sacrifices access to the upper 16K of
|
||
|
|
your AT28C256 for the sake of simplicity because it uses A14 as
|
||
|
|
the chip selector. Therefore, addrs 0x0000-0x3fff belong to the
|
||
|
|
first chip and 0x4000-0x7fff belong to the second.
|
||
|
|
|
||
|
|
You can see the schematic in dual-at28.jpg.
|
||
|
|
|
||
|
|
The schematic enables WE on both EEPROMs, but in my actual
|
||
|
|
prototype, I hard-wired the first chip's WE to high because I
|
||
|
|
never want to write to it, despite bugs I might introduce in
|
||
|
|
hardware or software (I try a lot of dangerous stuff on my
|
||
|
|
machines...).
|