18 Jul
2004
18 Jul
'04
1:25 a.m.
Hi Tony,
That's correct. There are also two language cards, one just has 16k to
replace the ROM's, and one has more memory which can be bank switched
into the 16k ROM address space.
So - I have a
bit of a paradox : the "2kb/2716" label suggests
ROM's, and the 64k of RAM on the mainboard also indicates that
all the RAM is on the lower board, however the ROM strings
suggest that this may be the only ROM.
IIRC, a real Apple ][ has up to 64K RAM (48K on the mainboard, 16K on a
language card) and some ROMs. The ROMs are bank-switched with the top 16K
(Language card) RAM. It sounds like you effectively have a built-in language
card (that would
be quite sensible), and you have RAM in place of the ROM (possibly to get
round Apple copyrights). The 5517 RAMs take the place of ROMs -- they're
loaded once on boot-up, and then contain the resident BASIC, etc. The
EPROM you have sounds like a bootloader for these RAMs.
Thats exactly what I am thinking.
Still trying to figure it out - never gets as far as trying to read the
disk - does chip select the ROM and appear to read some code from it,
but does not make it much further.
Btw, do you (or anyone) have the pinout for 4564 DRAM's? I'm wondering
if they are in backwards (as noted previously, someone "worked" on this
unit) - 16 pins, showing +5 on pin 8 and Gnd on pin 16 - backward to
most chips, although I do recall there were some memory chips with odd
power... Lack of working main RAM would explain it's behavour.
Regards,
Dave
--
dave04a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools: www.dunfield.com
com Vintage computing equipment collector.
http://www.parse.com/~ddunfield/museum/index.html