Grasshopper wrote: ↑Sat Jan 06, 2024 3:17 pm
[*]In your previous reply, you said that the HS & VS VGA signals could be connected directly. Are you saying that they should definitely be connected directly, or are you saying that ideally they should be connected using 120R resistors but that you can get away with connecting them directly?
I'm currently connecting them directly.
HOWEVER...
The pins I'm using for the dedicated VGA interface have 1.8V levels, which is far from ideal. They really should be level shifted up to proper TTL levels.
Adding a 120R resistor given a small amout of additional protection to the FPGA, but will potentially reduce the levels even further.
You really need to test this with the monitor you are intending to use.
Or better still, use HDMI. And as a bonus you'll get more colours.
On the Atom Core (but not currently on the Beeb Core) the VGA signals are duplicated to a second set of outputs called the gpio bus, and these outputs are 3.3V levels. But these outputs are multipurpose. So if you ever wanted to use the 6502 bus tracing feature (e.g. for debugging a machine code program) you would loose this copy of the VGA signals.
Sorry it's a bit complicated, that really just reflects this being more of an experimental project!
Grasshopper wrote: ↑Sat Jan 06, 2024 3:17 pm
[*]The Acorn Atom (and BBC Micro) only has mono audio output. But I've just realised that all of the speakers that I'm likely to connect this board to are in stereo. So can you advise me how I can connect a mono signal to stereo speakers so that the mono signal is output to both speakers simultaneously, with no loss of volume or quality?
You can just connect the mono output signal to both the left and right line level inputs at the same time. There shouldn't be much of an impact on volume or quality, as the input impedence of a line level input should be quite high.
Grasshopper wrote: ↑Sat Jan 06, 2024 3:17 pm
[*]For the sake of completeness, I'd also like to wire up the ps/2 mouse connector. But I'm not sure how to test it. Is there any Atom software that actually supports a mouse?
Kees has written a ROM called Atomic Windows that uses the mouse. I think there are some demos written for Atomic Windows.
If you just want a quick test, this should print the mouse X/Y coordinates:
I haven't tested this myself, but if it doesn't work I can investigate.
Grasshopper wrote: ↑Sat Jan 06, 2024 3:17 pm
[*]Is this project now essentially finished, at least from a hardware perspective? The reason I ask, is because at some point, I'd like to transfer the design to vero board. But I won't do that just yet if there are likely to be further changes or enhancements.
This is a hard question to answer. I'm not actively working on it, but if anyone reports an issue than I'll try to fix it. I'm not planning any changes to the pin assignment.
Grasshopper wrote: ↑Sat Jan 06, 2024 3:17 pm
[*]Once the Atom core is fully working, I'd like to flash the BBC Micro core to my second Tang Nano 9K. Should the ps/2 keyboard etc. be wired up in exactly the same way for that core?
Yes, the idea was to make the two cores compatible, so they use identical .cst files.
I have a single breadboard that I'm using for both systems. Eventually I'll get around to designing a PCB, if someone else doesn't do that first.
Dave