25 Nov
1998
25 Nov
'98
7:11 a.m.
o EPROM enable switch.
Where is the original PROM ?
Use a part of the EPROM constantly maped at $0000 or add an
1824 32x8 RAM ?
o Circuit to ghost EPROM at $0000 until first address
access at $8000
I still would go for a better decoding - just the high bit is to short.
Maybe there are some spare gates to use ?
And I still would like to combine the shadow and boot option.
o Sockets for two 1822/2101 256x4 SRAMs, the same
style used by
the original Elf.
Esential to be as close as possible to the original design.
o A 1851 programmable input/output port -or- a pair
of 4508 latches
wired as one input and one output port (as in the COSMAC VIP)
I would go for two 1852 Ports. They use only one adress each.
o A 1854 UART
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.
o Either a dual 4042 address latch or a single 4508
latch. One or
the other is needed to implement more than 256 bytes of memory.
This would be optional in a machine built with dual-256x4 SRAMs.
Isn't there already a fiting latch in the 18xx family ? (1883 ??)
I would prefer 18xx chips prior to all others.
o A pre-programmed 27256 with a "library"
of simple programs
(Accessible by enabling the ROM switch, setting the program
number in the switch register, then setting the control switches
to "run").
Did I miss anything? Any other suggestions? I will
not be including space
for an 1861 because I have been entirely unable to locate a source.
But maybe space for two (or better four) 1855 MDU. Playing with such
a beast is suposed to be a lot of fun. The same might be true for a
1879 RTC. These parts are still available.
Also I would like to have an additional 1852 (i/o selectable via
switch - but I only need output) to add an LCD display. Thera
are some real cheap displays available with a paralell ASCII
input - less than 25 USD for 16x2 characters.
Do we still have any interested parties? I have saved
the addresses of
all who have initially expressed interest, so I only really need to know if
these features are attracting people or putting them off.
Let's get serious, the Elf99 is not suposed to be the real thing, used for
real applications. It's just for the fun of doing it, and experimenting with
unusual concepts (unusula from todays view). When ever you want to
do real apps, any 6504+6532 or 68xx singlechiper will be more relevant.
Servus
Hans
--
Ich denke, also bin ich, also gut
HRK