Search found 566 matches

by mrtinb
Mon Jan 22, 2018 7:52 pm
Forum: Hardware
Topic: My first wire wrap: Wilf's AT keyboard interface
Replies: 18
Views: 544

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

Is the value of R2 (1m) correct? Looking at Wilf's schematic that seems right. Also, I would have thought that you would want to be pulling pin 20 (/CS) of U1 (28C256) to a logic low, not a logic high. Or am I missing something? Wilf's schematic is for 27C256. I've used a 28C256 in my design (actua...
by mrtinb
Mon Jan 22, 2018 5:28 pm
Forum: Hardware
Topic: My first wire wrap: Wilf's AT keyboard interface
Replies: 18
Views: 544

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

I'm trying to implement Wilf's circuit as mentioned in the first post. I hope I have not made any mistakes. I for the time being I have replaced the PICAXE18X with a few DIP switches just to see if it's working. After this circuit is working I will program an Arduino in place of the PICAXE18X. THE Z...
by mrtinb
Mon Jan 22, 2018 3:45 pm
Forum: Development
Topic: Help Wanted
Replies: 11
Views: 169

Re: Help Wanted

If you want to order from EasyEDA you click the [G]-icon to download your Gerber files. But instead of pressing [Download Gerber Files] you press [Save to Cart].
by mrtinb
Sun Jan 21, 2018 9:28 pm
Forum: Hardware
Topic: My first wire wrap: Wilf's AT keyboard interface
Replies: 18
Views: 544

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

Now I've connected it to a ZX81, but it gives me only white screen. It is a simplified version, that only has dip switches to select a button. (The PS/2 will be connected later when I program the microcontroller.) How can I debug this? I can read all pins on the EEPROM with a digital probe. The curr...
by mrtinb
Sun Jan 21, 2018 9:05 am
Forum: Development
Topic: Help Wanted
Replies: 11
Views: 169

Re: Help Wanted

And again pcbshopper.com is your friend. You can get them from allpcb.com with free shipping with DHL in 5 days for only $17.95. If you have trouble getting the gerber files saved on the library pc, and upload them to allpcb.com, you can just order the pcbs directly from easyeda.com for $18.98, but ...
by mrtinb
Sat Jan 20, 2018 8:34 pm
Forum: Development
Topic: Help Wanted
Replies: 11
Views: 169

Re: Help Wanted

If you have access to a browser, you can easily create schematic and pcb with https://easyeda.com/ . That's what I use.
by mrtinb
Wed Jan 17, 2018 9:42 pm
Forum: Development
Topic: old magazine article -- interesting ! ??
Replies: 14
Views: 396

Re: old magazine article -- interesting ! ??

It seems building this unit is useless unless someone has the content of the EPROM Operation System Software sold from the magazine.
by mrtinb
Tue Jan 16, 2018 7:11 pm
Forum: Hardware
Topic: My first wire wrap: Wilf's AT keyboard interface
Replies: 18
Views: 544

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

Wouldn't that limit to only 8 external devices?
$FE, $FD, $FB, $F7, $EF, $DF, $BF, $7F
by mrtinb
Tue Jan 16, 2018 5:27 pm
Forum: Hardware
Topic: My first wire wrap: Wilf's AT keyboard interface
Replies: 18
Views: 544

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

But wouldn't this interface conflict with any other device with A0=0? Wouldn't it conflict with any device with even I/O address?