RS232 - PS2

Ref RS232 – PS2 interface using a PIC12F675 a RISC 8bit chip.

Anyone know if this similar to the 32bit Arm chip for programming purposes?

Hmmm… “Is an 8 bit microcontroller similar to a 32 bit application processor?”

That depends upon how vague and inclusive your definition of “similar” is, but I’d be leaning towards “not especially”.

Does anyone remember any BBC / Arc code that deals with RTTY Navtex reception?

Try asking on Stardot perhaps?

https://stardot.org.uk/forums/viewtopic.php?t=24101

Thanks for your pointer to RTTY info- are there any examples around of the use of countdown timers on RISCOS?

What’s the Arc’s version?

.delay
LDA time
STA &FE68
LDA time +1
STA &FE69
LDA #32
.wait
BIT &FE6D
BEQ wait
RTS

That looks more 6502? BBC. BIT doesn’t ring any bells with me, though.

Yes, that’s 6502 code. The LDA and STA are blatant giveaways as the ARM, being RISC, doesn’t have an accumulator – you can use the register of your choice ¹.

BIT is basically the same as an AND, only it throws the result away. It’s intended for fiddling with the status flags.

I guess you’d probably want to use the HAL timer for this? What sort of interval speeds are we looking? If it’s like the Navtex sample here then live capture might be better handed off to a microcontroller that can do one job well, rather than a machine running an OS with non-deterministic responses.

There is, of course, another simpler solution. Just record the audio as a wav and interpret it afterwards. No need for any timers as you can track time by counting the audio samples, plus you can do whatever is needed to lock into the data stream, and it doesn’t need to be done in real-time (hell, you could do it in BASIC! ;) ).

¹ Protocol may dictate certain things, like being careful loading into R15, don’t use R13 or R14 unless preserved, and so on.

Yes 6502 code – so far, I have have found ref to the Iyonix using count down timers – but no info how to use them.

There is some work on higher resolution timers, but it seems to have stalled.
https://gitlab.riscosopen.org/RiscOS/Sources/Kernel/-/merge_requests/63

On older systems, usually IOC Timer 1 is available for you to use. Whether that’s an appropriate thing depends on what you’re actually trying to do.

IOCTimer1

Yup, which I used for this: