SC720 RomWBW boot issue

[Gordon Wainwright]

Hello

I have built up my SC720 and added the jumpers as in the comprehensive instructions.

The SCM will boot up, showing the sequence of lit LEDs.

Unfortunately, no LEDs light up when I throw the switch to boot the RomWBW and hit reset.

The SCM boots in either socket.

I have no means of checking the RomWBW device for functionality away from the SC720. 

Any ideas as to what needs to be corrected?

After I had varied the bootup sequence, I inserted all ICs but failed to include the jumpers. At no time has the JP2 had a jumper inserted.

The complete kit of parts was purchased from Tindie.

[Steve Cousins]

Hi Gordon

I assume, with SCM, the LED sequence runs once at reset and does not repeat.

Have you connected the serial port to a PC/terminal yet?

If so, does SCM function correctly?

I can't think of a way to check the contents of the RomWBW chip but I'll give it some more thought.

Steve

[Wayne Warthen]

This is very odd.  RomWBW turns on the first LED very early in the startup sequence.  If SCM is working, then your hardware is generally OK.  Other than some kind of ROM corruption, I don't know why you would not get and LEDs at RomWBW startup.

Thanks,

Wayne

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[Steve Cousins]

I've just checked a couple of the ROMs in my stock of SC720 kits and they look okay. I'm sure your kit came from this batch. While it is not proof that your RomWBW ROM is correctly programmed it is at least reassuring.

Steve

On Thursday 21 March 2024 at 18:58:36 UTC Gordon Wainwright wrote:

[Gordon Wainwright]

Hi
Many thanks for responding to my RomWBW problem;
I don't discount the possibility that I may have corrupted the ROM; the write-protect jumper was not in place initially. (Is this possible?)

To take one step further back.
There was no LED sequence for the SCM on the first power-up with all ICs in situ.
This failure was due to the '273 IC; reinserting it overcame the issue.

The fact that SCM runs in either socket gives me confidence that the hardware is functioning.

I have yet to connect the Serial-USB module to serial port 0 and set up Tera Term or PuTTY.

I want to use a Virtual Windows 11 installation running my Apple Mac, but it doesn't look like it will succeed.

I am in the process of obtaining a cheap laptop that runs Windows 11 natively.

I should then be able to use SCM once I've got one of those terminal apps working.

To return to the RomWBW issue, checking the ROM contents would be a straightforward task if I had the kit.

The fact that I don't see any LEDs light up when booting RomWBW suggests the IC is damaged.

 Advice on some ROM flashing kits would be welcome.

Gordon

[Richard Deane]

For the future, perhaps Wayne could embed a checksum in each flavour of romwbw or just a published checksum config table , and SCM could display or calculate the checksum. Then user can compare from the build table of checksum with configuration  flags to verify it matches their device.

Richard 

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[Steve Cousins]

Hi Gordon

I think trying the serial connection would be helpful. If that works then there is quite a lot we can do using SCM.

I use a TL866 programmer. I think it is quite a popular bit of kit in this community. My website has checksum details for each firmware issue I supply, as well as downloads of the ROM images.

You mentioned earlier you powered it up without jumpers. Even with the Flash protect jumper missing and the write signal to the Flash ROM floating, I doubt it would be corrupted as the write enable sequence is unlikely to occur by chance. It is possible I made a mistake programming the chip but as the others in my stock are okay I would expect your chip to also be okay. But it is always possible.

I think it is possible there is a fault in the memory management circuit. SCM only requires the memory configuration that occurs with a hardware reset. It does not rely on programming the memory bank select circuit. RomWBW may require this circuit to work to get to the point of lighting LEDs. I'm not sure without digging through the code. A fault around U5 could possibly fit the symptoms.

If you can get the serial terminal running there are things we could try to identify the problem. I don't currently have much in the way of diagnostic software for SC720 class of design but now might give me a reason to write some.

Steve

[Gordon Wainwright]

Steve

I've found what needed to be corrected.

My oversight when I said that SCM worked in BOTH sockets.

The problem was U4 pin 4 (A12) o/c.

A quick dab with the soldering iron solved the problem.

All LEDs turn on in sequence and remain on, when ROMWBW is selected for booting.

Both ROMs in circuit, boot up as expected now.

The laptop arrives later today.

Thanks for the info on the Flashing kit.

My thanks to all who have responded to this thread.

Gordon

[Steve Cousins]

That's good news. So often the way that a problem ends up being a simple assembly issue. Still, that is much better than it being a damaged or faulty component.

For what it is worth, I use Tera Term.

Steve

[Derek Cooper]

Did you put the write protect jumper on ? it can be a bit random without it

[Wayne Warthen]

On Fri, Mar 22, 2024 at 12:13 AM Richard Deane <rwd...@gmail.com> wrote:

For the future, perhaps Wayne could embed a checksum in each flavour of romwbw or just a published checksum config table , and SCM could display or calculate the checksum. Then user can compare from the build table of checksum with configuration  flags to verify it matches their device.

Yeah, that is a good idea.  I will see if I can generate the checksums automatically as part of the build process.

Thanks,

Wayne 

[Wayne Warthen]

After trying a few things, I settled on a different approach.  There is a short, human readable label for all ROMs imbedded at the start of the ROM image.  It already had the version of RomWBW.  I have added the configuration information to this.  So, to verify a ROM contains what you intend, you can just dump the first page (256 bytes) of the ROM.  If SCM has access to the ROM, it can do this.

Thanks,

Wayne 

[Mark Cohen]

Basically when in doubt reflow all solder joints.

My technique is to reflow when I think I am done or simply to reflow each component before I move on to the next. I can truly say my projects usually work on the first try now.

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