Search found 585 matches

by mrtinb
Sat Feb 24, 2018 12:57 pm
Forum: Hardware
Topic: Memotech HRG: ROM mirroring!
Replies: 14
Views: 283

Re: Memotech HRG: ROM mirroring!

Under normal circumstances you cannot replace the ROM at 0000-0fff with the shadow RAM because the I register needs to be set to $1E in order for the character generator to work. If you change I register then the characters on screen will be messed up, psuedo hires. This using the lower bit of the ...
by mrtinb
Sun Feb 18, 2018 12:25 am
Forum: Welcome Area
Topic: ANDRE*** is back!
Replies: 13
Views: 371

Re: ANDRE*** is back!

Hi Andre*** This is great news. You are a famous name among here. I was very pleased to read your newsletters ZX91 when I found them 2.5 years ago. I was impressed what was possible with a ZX81 and an Alphacom. The output of the software Word Sinc II set me on a quest to find that program. After req...
by mrtinb
Tue Feb 13, 2018 8:31 pm
Forum: Hardware
Topic: My first wire wrap: Wilf's AT keyboard interface
Replies: 43
Views: 1442

Re: My first wire wrap: Wilf's AT keyboard interface

gammaray wrote:
Tue Feb 13, 2018 7:40 pm
I hope I am not hindering that
In no way. I appreciate your interrest.
by mrtinb
Tue Feb 13, 2018 9:56 am
Forum: Hardware
Topic: My first wire wrap: Wilf's AT keyboard interface
Replies: 43
Views: 1442

Re: My first wire wrap: Wilf's AT keyboard interface

Currently I think the problem lies with the "diode OR gate" where both A0, RD and IOREQ has to be low, for OE on EEPROM goes low.

It needs a little more time and a clear mind. Today that is FALSE. ;-)
by mrtinb
Tue Feb 13, 2018 9:50 am
Forum: Hardware
Topic: My first wire wrap: Wilf's AT keyboard interface
Replies: 43
Views: 1442

Re: My first wire wrap: Wilf's AT keyboard interface

On your schematic Is /WE the same as programming voltage? Vpp? Should it be low instead...27C256.gif I didn't realize there were so many balls on the table. The text drawing is the original one from Wilf Rigter that uses an EPROM. I've modified it to use an EEPROM seen the the schematic in former p...
by mrtinb
Tue Feb 13, 2018 9:49 am
Forum: Hardware
Topic: My first wire wrap: Wilf's AT keyboard interface
Replies: 43
Views: 1442

Re: My first wire wrap: Wilf's AT keyboard interface

gammaray wrote:
Mon Feb 12, 2018 1:31 am
This looks suspicious to the left of the yellow A5-A13 connection.
I'll look into that
by mrtinb
Mon Feb 12, 2018 12:18 am
Forum: Hardware
Topic: My first wire wrap: Wilf's AT keyboard interface
Replies: 43
Views: 1442

Re: My first wire wrap: Wilf's AT keyboard interface

I assume it’s GND on the 28C64 EEPROM I’m using. Look at previous post for my schematic
by mrtinb
Sun Feb 11, 2018 10:28 pm
Forum: Hardware
Topic: My first wire wrap: Wilf's AT keyboard interface
Replies: 43
Views: 1442

Re: My first wire wrap: Wilf's AT keyboard interface

I just realized my EEPROM never gets Chip Enable signal, at the Arduino controller is not yet implemented. I need a switch for Chip Enable instead.

Back to the drawing board. :)
by mrtinb
Sun Feb 11, 2018 10:05 pm
Forum: Hardware
Topic: My first wire wrap: Wilf's AT keyboard interface
Replies: 43
Views: 1442

Re: My first wire wrap: Wilf's AT keyboard interface

I've changed the EEPROM, and checked that A13 is not connected to anything other than A5 on the EEPROM. It didn't fix anything.

Can anyone suggest why A13 is Pulse-Low, when everything else is Pulse-High-Low?

When the card is not connected to the ZX81, then A13 is Pulse-High-Low.
by mrtinb
Sat Feb 10, 2018 6:27 pm
Forum: Sinclair Misc
Topic: The Future of Sinclair ZX World
Replies: 57
Views: 3328

Re: The Future of Sinclair ZX World

I’ve just made a full mirror of the site. It took 25 hours. It is read only. No database. So you will be able read a copy of the site while it’s down.

http://zxw.s3-website-eu-west-1.amazonaws.com