SG8 continuous reset

[layman]

Hello,

I facing a strange issue of continuous reset on my S9S08SG8 board. The SG8 seems to be resetting continously as the scope connected to reset pin shows a square wave of about 25Khz. To isolate the problem I connected only VDD and GND with a 10K pull up to RST. I can still see a 25Khz squre wave on RST.

If I pull up the BKGD/MS pin while booting, RST shows steady 5 V. P&E is unable to program the IC.

Am I missing something ? 

Thanks

Pramod

[layman]

Correction : It should be

If I pull down the BKGD/MS pin while booting, RST shows steady 5 V. P&E is unable to program the IC.

instead of

If I pull up the BKGD/MS pin while booting, RST shows steady 5 V. P&E is unable to program the IC.

Thanks

Pramod

[pgo · Accepted solution]

Dear Pramad,

The symptoms you describe are usually caused by a COP timeout or Illegal instruction reset.  Judging by the frequency I suspect the latter.  Holding BKGD low during power-on causes the device to enter BDM mode disabling the COP and instruction execution.  This can occur if the chip is blank or programmed incorrectly.  Once programmed it usually isn't a problem.

I would expect that the P&E BDM would be able to  to do the same thing (i.e. hold BKGD low) while prompting you to cycle the target power. 

Does the P&E BDM work with other chips?

If so try the following sequence:

Hold BKGD low while powering on (use a 100R resistor if it works to avoid damaging the BDM).

Connect the P&E BDM.

Release the BKGD pin.

See if the BDM can connect now.

bye 

Message Edited by pgo on 2009-10-29 05:11 PM

[layman]

Thanks PGO !!!

Holding the BKGD low manually seems to solve the problem. I expected the P&E to take care of this but for some reason it doesnt.