J. Guy,

The WDT requires a minimum reset pulse width of 50ns. The P89C51RX2 ALE minimum pulse width is given as 10ns at 20MHz by Philips.

All of the signals involved were already running through the FPGA, so this was an easy solution.

Gavin,

Chemists(and engineers) are typically smart people. Flash Magic is a great tool that is very easy to use. You can generate a settings file so all that they need to do is; start the target in the bootloader mode, double click on the settings file, and click start. The only trick is that you need to make starting the target in the factory bootloader mode easy for them. That can be done via hardware or software. Flash Magic can even send a command to your firmware to cause it to vector to the factory bootloader.

PS: I don't work for ESAcademy.

Cory Spackman