Monday, June 30, 2008, 01:07 PMI pulled out my wreck-of-a-ZX-Spectrum-+2B out of a box with spare parts.
Fortunately this one was working, although I had used it before to experiment with (case was in 3 pieces, taperecorder disconnected, and more).
So I inserted the PC keyboard interface, and yes!!
No... not all keys worked.. pity.......
It seemed dataline D0 did not function correctly.
But I also noticed the internal keyboard did work simultaniously, although that should not be possible with my current design of the interface.
I contacted the very happy Miguel from Spain again (you may know 'they' won the European soccer-competition yesterday!) to confirm our thoughts that the +2A/B/3 ULA has a much stronger coupling with the Z80.
This is caused by a lack of resistors on D0..D7 so that external interfaces almost can't compete with the data supplied by the ULA.
The only attempt of solving this problem without modifiing your +2A/B/3 is to use a databus driver on the interface that has a very low impedance, or shortcircuits the datalines to 0V when needed.
But.. this is not without the risk the +2A/B/3 ULA is damaged.
Our first attempt to solve this problem with cause is to replace the 74LS541 by a 74HCT541 which has the same function, but uses MOSFET transistors with very low impedance.
This might work well!
I ordered the pieces an hour ago, but it may take up to two weeks to arrive :( SORRY!!!
Friday, June 27, 2008, 06:05 PMThis will be the PCB design for production:
As you can see, I rotated the PS/2 connector upwards, so the keyboard connector is inserted from top instead of from the right.
This way there is no hassle with the power connector from the Spectrum.
+2A/B/3 testing will be next! (this evening maybe)
After that the production will start!
Sunday, June 22, 2008, 08:06 PMI must have a complete partlist with prices somewhere...
Let's .. check... ahh yes, here it is:
If I build 25 pieces, the price would be only 25 euro .
I'm not sure if that's with silk screen finishing on the PCB or not..
(Check check... )
Ok, so that INCLUDES a silk screen, which is not on the prototype (the pictures in previous messages show the bare PCB without silk screen and coating).
If you are already interested, mail me and I will put you on my list.
Sunday, June 22, 2008, 08:02 PMI also just finished some tests on DivIDE, and it also works great and without any problems.
So I've succesfully tested the combinations of:
- ZX Spectrum 48K / 128K
- MB02 or DivIDE
- Kempston Mouse Turbo
- The new PC Keyboard interface
I have not yet tested the ZX Spectrum +2A/2B/3 with these devices.
I do have a grey ZX Spectrum 128K and a ZX Spectrum +2A (or B, have to check), so if anyone likes to know, contact me.
Sunday, June 22, 2008, 02:42 PMWow, unbelievable, it all works together!
Words cannot explain, you have to watch for yourself.
So here's a video: http://www.youtube.com/watch?v=F4vBnpmkRwY
And some impressions: