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Topics - GeeMott

#1
Another real hair-puller for me.  I have a mature, stable design based on the 89LV51RC2.  When that part was discontinued, I moved to the -RD2.  When I program them with the same old code, they work fine -- at first.  Some of them (3 so far out of 10) just spontaneously erased themselves after a few days.  I even tried setting the security bit and adding a serial number as write protection, to no avail.  I put the failed board on Flash Magic, and saw the security bit was still set, but the part was otherwise blank.

Suppose I have a stack leak or wandering program counter in my code, that was never found because the RC2 had less program space -- something that was benign before, but now isn't.  Is it possible to access a built-in "erase all" subroutine by accident?
#2
I have a year's supply of boards that were programmed successfully with FM (thanks in part to your help). Yay. But now they need to be upgraded, and they just refuse to be reprogrammed.  I'm using the 89LV51RC2.

Here's the symptoms.
1. It tells me I'm using the wrong device, but I'm okay with that. Still, it's a symptom.
2. It goes through the whole program cycle, but takes twice as long as normal.
3. It fails verify on address 0x0001.
4. When I read the flash contents back, I see that it has changed the byte at address 0x0001 from whatever it was, to 00.  Everything else appears to be the same -- unchanged from the original program.  Even the byte at 0x0000.
5. If I try to update the bootloader (to eliminate symptom 1) it appears to run the whole thing, but then times out at the end.  And I still get symptom 4.
6. If I try to erase the whole chip, it comes back with a success message way too fast, and no erasure.

Of course I need not point out that I used to be able to do upgrades with no problem, been doing it for years, and that nothing I know of has changed, except maybe the batch of the microcontroller.  Is there a known problem with a recent batch?  Or have I got a serious brain fart going on?

I must also point out that I am not using any security bits or serial number protection. I use 6 clocks on both the original and the upgrade.

Anybody got an idea for some tests I can run, and some way to salvage these guys?
#3
P89V51Rx2/P89LV51Rx2 / Why won't 89LV51 enter ISP mode?
November 17, 2006, 06:54:14 AM
uC: P89LV51RC2FA, PLCC44 pkg
VCC = 3.3V at pin 44 verified
VDD = GND at pin 22 verified
EA pin 35 at VCC verified
PSEN pin 32 is floating
XTAL1 pin 21 has 12.5 MHz square wave, 3.3v/GND
XTAL2 pin 20 floating
RST pin 10 has 10uF to VCC, 8250 ohm to GND
TXD pin 13 is, at the moment, floating

Start FlashMagic, see 4.808 KHz square wave, 3.3v/GND at RXD pin 11.
Bring RST to VCC (approx 2 nS rise time) for a time anywhere from 400 mSec up to several seconds.  Fall time is approx 100 mSec.

Nothing EVER appears at TXD, which stays at 3.3v. (Once it responds, I will reconnect it to my 232 driver and go from there).

I don't imagine the problem is in FlashMagic, but What Am I Doing Wrong?