Re: ][+ ROM Card

["Terence J. Boldt" <ter@interlog.com>]

>You have to be rather careful if you have two of these cards installed
>(or one at the same time as the language card in slot 0 of a ][+),
>because they all use the INHIBIT signal to override the motherboard
>memory.  If two of the cards are active at the same time, they will
>cause a data bus clash.


Whoa!  I didn't say I had two cards installed, I said I have two cards.
Both cards work, one at a time.

>I don't recall offhand whether they try to use the DMA IN/OUT chain to
>avoid conflicts, but even then they would only be fully safe if in
>adjacent slots.

I don't think they do use the DMA lines.  I'm certain you are right that
using two ROM cards at the same time would fail.

I see you know your peripheral slots.  Jumping topics here, I am currently
building a bootable EPROM card and it's quite flakey.  Perhaps I could bug
you for help sometime.  The 256 bytes of ROM at Cn00 - CnFF on my home-built
card work fine, in fact it even gets executed by the auto-start ROM.  I use
two ports in the C08+n0 to C08+nF range to set 8-bit latches (programs the
16-bit address for my big code ROM) and then one other port (actually
several) read the data from my big ROM.  The only problem I get is that if I
read the ROM too fast (not the 256 byte ROM) the latches seem to get
corrupted and then suddenly I'm reading from the wrong address.  I wrote a
program in BASIC to read the ROM off my card through the ports and it works
fine - I have access to 512K of ROM.  From assembler, I get over 50% failure
rate.  If I perfect this card, I'm going to have a dozen or so manufactured
for fun.  I talked to a couple companies and I can have the PCB's made for
about $35 - $40 Canadian each (plus then I have to buy and solder in the
components myself).  Anyways, if you have ideas to help me or just want to
know more about the project, let me know.


-- Terence J. Boldt