The only trouble I see with going to the 8085, is the loss of the status byte. It can be partially recreated by decoding the state lines, which have to be done anyway to differentiate I/O vs Memory access. But a "Stack" and "Inte" signal can not be gotten.
The main purpose of this board was to be compatible with the front panels of the ALTAIR and IMSAI.
Does the group want to drop that *full* compatibility and go with an 8085 board? I put it to a vote.
The 8085 can function with limited functionality with the front panels. Here's a break down of the front panel and what's loss.
+ indicates signal can be produced
STATUS BUS
+MEMR
+INP
+M1 (fetch)
+OUT
+/WO
+HLTA
-STACK (no more indication of STACK operations, no big loss)
+INTA
CONTROL BUS
-INTE (no indication of Interrupts enabled, no big loss either)
+HLDA
-WAIT (no indication of a WAIT mode... is that right? or am I missing something in the data sheet?)
Further, the RUN/STOP function will not stop on a M1 (Fetch cycle). this will cause erratic behavior of the Examine/Next functions. Work around is to single step to an M1 function then use "Examine". This might be the biggest down fall of the 8085 CPU, but not the end of the world since the Z80 had the same problem with the old front panels, and many didn't care about it.
I can't say we are losing much, but everyone has their own opinions of what's important.
I put it to a vote and/or discussion.
Cheers,
Josh
From: rich...@verizon.net
Subject: Re: [N8VEM-S100:5635] Re: 8080a board
Date: Thu, 20 Nov 2014 10:33:20 -0500
To: n8vem...@googlegroups.comAll good ideas, especially the 8085 and the sense switch input. I wish the msdos board had a sense switch input.
Sent from my iPhoneSome notes for Ver one... To gain some room on the board....As suggested before....Use only 4 wire rs232 with max232a/tr202, removing need for +-12v ( 3 to 4 chip saving)Move to 8085, no need for +12 or -5v, less support chip needed... ( ~2 chip saving)Make board stand alone, no other boards needed to make it run... ( plus 1 chip)Fix upper address and data lines to bus issues . (Plus 2 chips)New ideas...Replace 8212's with 74als logic (~ 3 chip saving)Replace ram chips with one larger chip, (wasting part of the chip to save room if needed) 64k x 8 or larger like an as6c4008 with a poor man's mmu if their room on board...(use output port?) like zeta board.... (~ plus 1 to 2 chip saving)If room, allow room for a dip switch with pull-ups on input port.... (~ plus 1 chip)Just my ideas from building the board....i~~ _/) ~~~~ _/) ~~~~ _/) ~~~~ _/) ~~iTom LafleurOpps, thanks for letting me know... I guess it's a cut n paste error or just an over sight.
Date: Wed, 19 Nov 2014 16:34:41 -0800
Subject: 8080a board
From: laf...@lafleur.us
To: crus...@hotmail.com
fyi...It appears that UART1 at A5 is connected to COM1 port, P1/P2 on the board, but the schematic say its connected to P3/P4
--
~~ _/) ~~~~ _/) ~~~~ _/) ~~~~ _/) ~~
Tom Lafleur
--
You received this message because you are subscribed to the Google Groups "N8VEM-S100" group.
To unsubscribe from this group and stop receiving emails from it, send an email to n8vem-s100+...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
--
You received this message because you are subscribed to the Google Groups "N8VEM-S100" group.
To unsubscribe from this group and stop receiving emails from it, send an email to n8vem-s100+...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.--
You received this message because you are subscribed to the Google Groups "N8VEM-S100" group.
To unsubscribe from this group and stop receiving emails from it, send an email to n8vem-s100+...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.