Search found 19 matches

by gesari
23 Apr 2019, 13:45
Forum: Hardware and software hacking
Topic: High resolution mode?
Replies: 25
Views: 1073

Re: High resolution mode?

I think the vertical lines are due to the propagation delay of the register. When clock changes to high the multiplexer switches first, showing a wrong value before new valid data comes out a few nanoseconds later. Also the multiplexer is built around AND/OR gates, and there are transients when the ...
by gesari
21 Apr 2019, 21:13
Forum: Hardware and software hacking
Topic: High resolution mode?
Replies: 25
Views: 1073

Re: High resolution mode?

And about the delays, these also depend on the data being added. The worst case is when the carry propagates from low adder to high, for instance for a $ff + $01 or $00 - 0.
by gesari
21 Apr 2019, 20:52
Forum: Hardware and software hacking
Topic: High resolution mode?
Replies: 25
Views: 1073

Re: High resolution mode?

Well, I can redo the board with this palette:
videodoubler3.gif
videodoubler3.gif (19.76 KiB) Viewed 98 times
videodoubler3_lay.gif
videodoubler3_lay.gif (12.87 KiB) Viewed 98 times
BTW, I was also not very happy with the many 157s needed for the selectable mode...
Maybe It would be a good idea to test the circuit on a breadboard before making a PCB...
by gesari
21 Apr 2019, 09:55
Forum: Hardware and software hacking
Topic: High resolution mode?
Replies: 25
Views: 1073

Re: High resolution mode?

Yes, an XOUT bit could be used, but this means to connect a line to another socket.
The circuit with the HSYNC mode latching could be:
videodoubler2_sch.gif
videodoubler2_sch.gif (65.65 KiB) Viewed 23 times
Here the bit storage is dynamic (C4: a 1-bit DRAM :)
by gesari
21 Apr 2019, 08:08
Forum: Hardware and software hacking
Topic: High resolution mode?
Replies: 25
Views: 1073

Re: High resolution mode?

I think the main application for a 3-bit, 320 pixels per line, mode would be text because it will allow 52 characters per line. The above circuit is very simple and doesn't allow for mode switching, but this can also be done with more multiplexing and a control bit. Then the video mode could be chan...
by gesari
20 Apr 2019, 15:26
Forum: Hardware and software hacking
Topic: High resolution mode?
Replies: 25
Views: 1073

Re: High resolution mode?

Meanwhile I worked a little on the original tocksin idea, and I think a convenient way to change the video mode to 320 pixels per line is to solder a socket for U37 (the output register) and then instead of plugging on it an HCT377 we plug this little board: videodoubler_sch.gif videodoubler_lay.gif...
by gesari
20 Apr 2019, 09:22
Forum: Hardware and software hacking
Topic: High resolution mode?
Replies: 25
Views: 1073

Re: High resolution mode?

Isn't a problem. I tough we can make the clock waveform more square if we put a resistor in parallel with C2 instead of replacing U1 by an HC04. But this is still untested. I simulated the oscillator using Spice and it seems to work, but the circuit I simulated is quite different from the real one, ...
by gesari
19 Apr 2019, 13:40
Forum: Hardware and software hacking
Topic: High resolution mode?
Replies: 25
Views: 1073

Re: High resolution mode?

Could you check if the resistor does the trick? I got no equipment here to test it, and simulation is not always like reality...
by gesari
19 Apr 2019, 10:23
Forum: Hardware and software hacking
Topic: In Circuit EPROM emulator and debugger
Replies: 2
Views: 60

Re: In Circuit EPROM emulator and debugger

A first schematic is attached.
by gesari
19 Apr 2019, 09:27
Forum: Hardware and software hacking
Topic: High resolution mode?
Replies: 25
Views: 1073

Re: High resolution mode?

I think the easiest way to get an 50% duty clock is to connect a 1k2 resistor in parallel with C2. This will also lower the oscillation amplitude at the inverter input (pin 1) avoiding negative voltages. And I see no problem with slow RAMs. Even the 70ns part has a write pulse width of 50ns, less th...