The Sinclair QL Forum

Dave wrote:I'll pull it out of the drawer tomorrow and identify the part that does the job of the 8049. That part. It was programmable, and lost its program.

You mean the PIC17C44, Dave? It has an EPROM for the code. I guess it's possible that in 27 years it might fail.

I was thinking of verifying with a scope that the onboard osciilator works. And I guess one thing to try after that would be to hook up the logic analyzer to some of the output signalling pins of the PIC to see if it actually is doing anything.

Dave wrote:I'll pull it out of the drawer tomorrow and identify the part that does the job of the 8049. That part. It was programmable, and lost its program.

I believe it's a 17 series Microchip PIC - 17c42 or something like that - these are flash programmable parts - I am not sure on the retention period for the program - would have thought it was a fairly long period - but it's possible the component was not 'over' programmed and so may have been hot or cold when programmed for instance. The chip pretty much does everything. It's a shame there's not "heartbeat' time LED or signal that can be monitored on it - Except perhaps to monitor the IPC comms lines in the QL and see what pattern is happening on there. At the end of the day - the thing has to 'talk QL'

Yes, it's a PIC 17C42 on the SuperHermes - But it doesn't have flash memory, but OTP (one time programmable) EPROM. When the program is gone, it's done with. (Data sheet is here).

I'd first check whether the chip still has some signs of life (clock, port outputs).

tofro wrote:Yes, it's a PIC 17C42 on the SuperHermes - But it doesn't have flash memory, but OTP (one time programmable) EPROM. When the program is gone, it's done with. (Data sheet is here).

I'd first check whether the chip still has some signs of life (clock, port outputs).

Thanks Tobias, I'll do that!

Interesting - for their OTP Eprom products - they are claiming 10 years retention:

https://www.microchip.com/en-us/product ... /otp-eprom

So it's possible that the program has corrupted over time. I must admit I thought these babies were flash, but then you'd still need the program code to reflash it if it was.

Hi,

It more likely the fault is on the IPC socket pins, try to inspect each pin, they are indivudally soldered to surface mount pads and damage can occurr to the pins, soldr pads or connecting tracks.

You might want to test the conductivity of the tracks from the IPC socket pins to the other components on the PCB.

To reflash the Superhermes rom code, will be hard due the code not being available.

I can ask Tony if he can supply me with the code and how to ipdate the flash rom.

Derek_Stewart wrote:You might want to test the conductivity of the tracks from the IPC socket pins to the other components on the PCB.

Thanks Derek, I did a visual inspection but will do a continuity test with a multimeter.

Derek_Stewart wrote: To reflash the Superhermes rom code, will be hard due the code not being available.

yeah, and the PIC version on SuperHermes has an EPROM so it's program-once. If the PIC turns out to be faulty, the only option is to get a new one but as you said: since the source is not available, it would need to come from Tony. I don't know what the lifetime of on-chip EPROMs is supposed to be but 27 years is a long time

Derek_Stewart wrote: I can ask Tony if he can supply me with the code and how to ipdate the flash rom.

Thank you Derek, that's extremely kind of you. Let's hope it's not the PIC but something else. I will test the continuity from pins to the PIC socket and also verify that the oscillator works. But, it would be really good to have a source of replacement PICs going forward!

If the source was available, then perhaps a newer flash based pic could be used, with perhaps a simplified design offering the same or better functionality?

There are several families to chose from, and many of the PIC's support hardware UART's, timers, Flash for both program and data storage.

If the EPROM code is available, it might be possible to 'refresh' the part but it will require skipping over the 'check blank' part as the part will not be blank. Usually some zero bits will revert to ones which is the un-programmed state.
I think there was a flash version of the same PIC chip but has also been obsoleted, though one might still find some for sale.

looks like document AN726 covers migration from pic17cxxx to pic18cxxx - but sadly can't find a copy of this on Microchip site anymore.

The pic18 range are flash based with 100 year retention, and would not require too much code tweaking to port across from the 17C42 device.

The problem is of course the source code...