More comments follow, but I've cracked some of my older Rainbow mags over
the last few days,and I found the company that sold the original XPNDR1
(and they had an XPNDR2 card as well, so you could still plug in your disk
controller...)
Robotic Microsystems
Box 30807
Seattle, WA 98103
The cards sold for $19.95 each, or $36 for 2 cards; at least that's what
they advertised for on page 139 of the January '86 Rainbow.
=-=-=-=-=-=-=-=-=-=-=-=-=
Rumor has it that Tony Duell may have mentioned these words:
>> Now, the first thing I'm going to do is put on a 74LS245 bus transceiver on
>> the data lines, and a pair of 74LS244's to buffer the address lines...
>
>Do you have a suitable signal to enable that 245 so that it only outputs
>data onto the CoCo's data bus when chips on the Xpander are being read?
>You don't want that 245 to contend with the ROM and RAM in the CoCo
Righto -- but I do want a ROM socket on my board, so I will have address
decoding (prolly for 8K, tho) to be able to access that.
I am *planning* on this being a large project... ;-)
As of right now, I have (2) 74LS244's buffering the address lines, but
there's more work on the way...
For a blick of what I currently have designed in Autocad (warning, it's a
130K jpg, and it's a *rough* design currently), go here:
http://www.30below.com/~zmerch/xpndr1/coco1.jpg
>Shouldn't be a problem. I've buffered E and Q many times without
>difficulty. As a purist, I'd use 2 sections of the same chip to buffer
>them (2 buffers in the same chip are likely to have similar propagation
>delays) but actually it shouldn't matter much.
That'll be the 3rd '244, which I have to map in after some of the address
decoding...
>Also look into the use of multiplexers ('151, '150, maybe with one extra
>NOT gate) as programmable 'gates'. I've used these to generate chip
>selects, buffer enable signals, etc in the past.
Thanks for the advice. I found that Fairchild has a lot of datasheets on
the web (in pdf format) so at least I can get pinouts & whatnot fairly
easily...
I have used multiplexers in one project in the past, so I should be able to
figure out how to use them in this new context... but it might take a
little brainpower on my part. ;-)
Altho I do enjoy playing with 74'series chips, if anyone out there has a
cheap CPLD/PAL/GAL programmer they wanna part with, keep me in mind! I'd
love to tinker with those... :-)
Laterz,
Roger "Merch" Merchberger
--
Roger "Merch" Merchberger --- sysadmin, Iceberg Computers
Recycling is good, right??? Ok, so I'll recycle an old .sig.
If at first you don't succeed, nuclear warhead
disarmament should *not* be your first career choice.
Received on Sat Sep 08 2001 - 11:26:10 BST
