[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: How do I add firmware to a card?
Alex Freed wrote:
> "David Wilson" <mcs6502@gmail.com> wrote in message
> 1168135177.894809.275730@i15g2000cwa.googlegroups.com">news:1168135177.894809.275730@i15g2000cwa.googlegroups.com...
>>
>>> The approach you mention is also worthwhile, although many uC's don't
>>> allow code execution from their volatile memory which may cause
>>> problems. It does open the door for some interesting modifications
>>> though.
>>
>> Good point. I forgot many (most?) uC use the Harvard architecture.
>>
> A notable exception is ARM. There are ARM7 chips with 8K or more of
> internal RAM and
> 64K or more or FLASH for around $4 these days. The only problam is they
> don't come
> in DIP cases.
I like where this thread is going. I've been giving a little thought to the
simple vs uC approach and I think I may have come up with a solution.
I see no reason why both the uC and the '811HC can't both be connected to
the bus. Well, with one or two concessions. That a '245(That's the
tristating bus buffer right? Headache...) be connected between the '811HS
and the apple bus.
The tristating for the '245 is controlled by the uC (perhaps also OR'd with
an address decoder), whereas the direction (R/W) is controlled by the apple
bus.
The uC is attached directly to the apple bus via it's PSP and a few extra
lines like a couple of address lines maybe?
At this stage there are a few solutions to the uC <-> 811HS communication.
#1: Cut out the '245 and do a kind of passthrough via the uC. This could
introduce timing and pin resource issues.
#2: Like #1, but keep the 245 and also have a direct BUS connection (via
the '245) between apple BUS and '811HS.
This is the most complex solution, but also my favourite as the uC can
monitor the bus passively even when disabled waiting for some kind of
enable signal. It also gets rid of the possible latency issues. However it
still keeps the possible pincount problem.
#3: Have a second '245 between the uC and the apple bus. Then reuse the PSP
port in normal IO mode for talking to the uC.
Anyway, that's my 2.02c.
I'm sure if GST could be put on ideas they would.
--
-----> http://members.dodo.com.au/~izabellion1/tristan/index.html <-----
===== It's not pretty, it's not great, but it is mine. =====