Hi John, Yes, I've got a V2-Ideas text file open. 1. MWRT is on the list. 2. This is not a good idea, some of the vintage boards decode the I/O using the high address lines (which I think is suggested in the 8080A Data Sheet). 3. A16-A23... should these be tied to GND or pulled down to GND with a resistor network? Thanks, Josh
Date: Thu, 31 Jul 2014 08:45:33 -0700 From: mon...@vitasoft.org To: n8vem...@googlegroups.com Subject: Re: [N8VEM-S100:4764] Progress with the 8080 board We should probably keep a "to do list" for V2 Josh.
1. Add MWRT with jumper. 2. For I/O port data out, address lines A8-A15 should be pulled low. (so only ports 0-255 addressed). 3. Address lines A16 to A23 always pulled low (in "master" mode)
Space is tight on the board as it is. #2 & #3 will require 74LS244's. You can shave off some space for the SD card transistor etc. As best I can tell E2 pin 10 does not do anything.
On Wednesday, July 30, 2014 5:24:51 PM UTC-7, Crustyomo wrote:
John, Thank you for testing this out and getting it working. I'm not having the same pull up problem on sOUT. This
board was designed for use with the ALTAIR and IMSAI FP boards, but I
agree and in V2, I will add mWRT generation and jumper select it for the
flexibility. You are right about the high address bus. The
8080A places the I/O address on both the upper and lower 8 bits. On my
initial version, I was decoding the upper 8 bits for use with I/O and
Memory banks, but later changed to add it's own decoder chip on the
lower address to support Z80 CPU's that might want to access this card
as a peripheral. What should I do with those upper address lines? Should I just ground them? or pull them high/low through a resistor network? Something for V2. Thanks for the schematic corrections, I have updated my copy and will release another revision soon. I
should also point out, if anyone is wanting to use the 16550 UART
chip, then RP2 must be changed to 47K. Thanks to testing with Fabio,
he found that the 16550 data bus output is getting pulled marginally
high with a 4.7K. The 47K will suffice to prevent the bus from floating
yet not interfere with the 16550's. Cheers, Josh
From: mon...@vitasoft.orgTo: cru...@hotmail.comCC: n8ve...@googlegroups.comSubject: [N8VEM-S100:4755] Progress with the 8080 board Date: Wed, 30 Jul 2014 11:44:12 -0700 Hi Josh solved the I/O problem (see below). Since a few others may be in the board assembly stage I thought I would write up my progress so far for the group! I am running the board in my “test box” that has no front panel. Just the V2-SMB and Propeller Console I/O. I always start with a minimal system so I don’t “blow out” board drivers etc. First one needs to remember that unlike the Z80, the 8080 does not treat the upper 8 bits of an I/O port the same way. On our Z80 board (and most others) the upper 8 bits are set ort Zero. Not so on this board. So on all the N8VEM/S100Computers boards (and perhaps others), ports need to be jumpered so that only the lower 8 bits are factored into port addressing. All our boards have this option. Not a nice solution since with 16 bit CPUs the ports appear on every 256 byte boundary. Setting the jumper K3 to 2-3 on the V2-SMB allowed the routine below to work correctly. The IEEE-696 upper address lines float. This will not allow 696 RAM boards to work unless they are adjusted. Our N8VEM/S100Computers boards generally have a jumper to ignore these lines but again will not work with 16 bit CPU’s. Our V2-SMB has an option to force these address lines to ground when this board is the master but release them for slave/16 bit CPU’s. Second the board does not generate the S100 MWRT signal. (On front panel systems, it’s generated there). One can be generated on the SMB with the JP11 jumper. There seems to be a problem with the sOUT signal (s100 Pin 45) on J8. It’s been pulled high all the time – at least on my board. I bent out J8 pin 6 and connected it directly to the S100 bus (bending out the pin connection on the extender board). I will try and follow traces to figure what is going on here. Minor schematic errors.Pins 8 & 9 of E2 are switched.Pins 1 & 19 of I8 and H8 should be labeled D-IN, D-OUT, etc. Still a work in progress, but wanted to save others reinventing the wheel. John From: John Monahan [mailto:mon...@vitasoft.org]
Sent: Tuesday, July 29, 2014 7:21 PM
To: 'Crusty OMO'
Subject: Problem with sOUT with the 8080 board
--
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. |