Search found 32 matches

by gesari
05 May 2019, 21:01
Forum: Hardware and software hacking
Topic: New form factor Gigatron.
Replies: 9
Views: 9767

Re: New form factor Gigatron.

I don't think a better layout will change the max clock frequency too much. Even if the data bus traces are 200mm shorter this length equals only to about 1.3ns propagation delay (wave velocity in tracks is more or less 1/2 the speed of light in vacuum). For a 15MHz clock this delay is only a 2% of ...
by gesari
29 Apr 2019, 14:32
Forum: Hardware and software hacking
Topic: Diodes
Replies: 3
Views: 3399

Re: Diodes

Hi, I ran some simulations of the diode AND gates and I was surprised to find how fast these gates are. This is the circuit I simulated. The 45ohm resistors takes into account the output resistance of the preceding logic (from an HCT138 datasheet), and the 10pF capacitor is an estimate of the gate l...
by gesari
25 Apr 2019, 19:10
Forum: Hardware and software hacking
Topic: In Circuit EPROM emulator and debugger
Replies: 20
Views: 13914

Re: In Circuit EPROM emulator and debugger

Hi, I completed the layout of the board. Finally I included a 10MHz crystal to get the micro running at 50MHz, so the 6.25MHz can be obtained dividing the clock by 8. lay_top_corner.gif Here you can see how the emulator gets placed on the EPROM socket of the Gigagtron. I had to make room at one corn...
by gesari
23 Apr 2019, 13:45
Forum: Hardware and software hacking
Topic: High resolution mode?
Replies: 38
Views: 38166

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: 38
Views: 38166

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: 38
Views: 38166

Re: High resolution mode?

Well, I can redo the board with this palette:
videodoubler3.gif
videodoubler3.gif (19.76 KiB) Viewed 8160 times
videodoubler3_lay.gif
videodoubler3_lay.gif (12.87 KiB) Viewed 8160 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: 38
Views: 38166

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 7892 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: 38
Views: 38166

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: 38
Views: 38166

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: 38
Views: 38166

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, ...