Sandeep,

Having worked with the '420 i can't say that i can replicate your symptom.

You generate a Reset and select whether you will execute from the stored program or the overlayed DEBUG Firmware.

Per Dallas;


"The ROM Loader mode is invoked by simultaneously applying a logic 1 to the RST pin, a logic 0 to the EA pin and driving the PSEN pin to a logic 0 level."

"If power were to cycle while the required input stimuli were present, the loader would be invoked on power up."

As prev. noted the A-2 revision has a fault which result in the advise from DALLAS;


"To enter loader mode, port pin P3.7 must be pulled high when the pin biasing combination of RST=1, PSEN=EA=0 is applied."

regards,
p