Re: Todd's ELF-ish to get an FDC #Homebrew #microboards

 

This 74HC688 method would work well for memory mapped I/O or memory mapped ROM but I'm not sure if it would be helpful if you needed both.


From: "cmdrcosmac" <cmdrcosmac@...>
To: cosmacelf@groups.io
Sent: Sunday, December 1, 2019 10:40:23 AM
Subject: Re: [cosmacelf] Todd's ELF-ish to get an FDC #Homebrew #microboards


I second Mike's recommendation for the memory mapping scheme.
I am running it on my current SuperElf expander. I've got IDIOT in a 32k EEPROM,
mapped at F800-FBFF. All the rest is RAM, in an AS6C1008 RAM 128kx8
from Digikey 1450-1017-ND  $2.77. It's hooked up exactly as in Mike's drawing.
 This also makes possible an arrangement described by Tony Hill in Ipso Facto # 21.
This allows you to locate a Monitor anywhere in address space and optionally
jump to it after RESET, RUN. I did it on my Elf. RESET, GO runs at 0000.
RESET, MONITOR, GO runs at F800. I believe the tradition of placing monitors at 8000
began with RCA's reset,run-u/run-p scheme. They seem to have done it on most of their
COSMAC boxes. This was OK when RAM was in short supply, but now it's limiting.
 I've run Basic 3 under both UT62 and UT71. The serial I/O routines are at the
same addresses. The Basic I have came with UT62, from Herb's site. I believe he also
has UT71/MicroDos. I haven't found a Basic made for MicroDos. I'm looking forward
to seeing your system work. You'll be computing like it's 1984!
Best,
-Chuck

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