25 Nov
1998
25 Nov
'98
2:44 p.m.
The basic elf was an 8bit address only design. The high order bites were
not latched.
It's memory was 256bytes (2101s) and an optional 32byte fuse prom. When
the prom was enabled it overlayed the first 32 bytes. The upper address
bytes were meaningless as no logic saw them. Very limiting design.
< > > o Circuit to ghost EPROM at $0000 until first address access at
$80
< >
< > I still would go for a better decoding - just the high bit is to short
< > Maybe there are some spare gates to use ?
<
< Wait a minute. We have been having an extensive offline conversation
< and you said that 32K of RAM and 32K of ROM is enough. It can be more o
< of either, at a cost of gates and complexity.
The VIP had 512bytes at 8000 and up to 4k at 0-0fffh/
< > Esential to be as close as possible to the original design.
<
< One vote for, several against or abstaining.
if you stay close to the quest design you cannot have much (and none of
the options) all of the options are desirable as most people added them
somehow or another.
< I'm not inclined to do dual 1852's. We you and I have discussed, the 18
< uses three ports, the switch/display is another port, leaving three lef
< over. While ports are scarce, they are no so scarce as to overshadow th
< benefits of a bit-programmable I/O port.
Use port one to select banks of ports (RCA app note). Then ports are
cheap and it only takes another latch.
ARE 1852 available and what do they offer over a simple cheap port.
< > Data transfer via Q is way more fun (Hi Alison :).
< > And since we don't need high speed transfer (2400 is ridicoulous i
< > we can do 110 :) a complete software solution is a great thing to do.
<
< I have no problems in principle with a software UART, but I do have
< something to say about the speed. 2400 baud is *not* a ridiculous
< speed, especially if you want to talk to an external device that has
< a fixed clock, say, a serial-to-LCD board. The other issue with a
< software UART is timing. If you use a hardware UART, it needs a
< crystal of a particular frequency, but the CPU does not. You can then
< "clock chip" the 1802 up (to use a Mac term) and not recode your serial
< routines.
Use the q led and EF1 for casette port. Uart for TTY/term.
< I still have yet to hear why the 1855 Multiply/Divide Unit is worth
< the real estate. Sure, it's a neat chip, but unless it has a purpose,
< I can't see including it.
Never mind finding it.
< but if I maximize the appeal of the standard I/O ports, I'm likely to se
< a few dozen. If I can't sell 60, I can't afford to invest in 100 PCBs.
And if its only the quest design I have one already. It's appeal wears
off real fast and it's was not designed with expansion in mind.
Allison