I was using Keil to program a Philips 89c51 chip last week to transmit data at 19200 bps. It was working perfectly, i got the data on the PC. I could also see the actual 0V - 5V waveforms on the TXD pin. This week I switched the chip to an Atmel 89c51 33 MHz one..using the same program but can't see thevoltages on the TXD pin. Tried putting a load resistor to ground, then I can see the voltages but the chip is now not speaking to my PC. Do I need to be doing something different..? thanks for all help..
No... I didn't switch the crystal. Just mentioned that the new chip supports 33 MHz. I am still using a 11.059 Meg crystal. The point is, the program is executing fine and alongwith writing to serial port, i tried toggling port pins and the timing of that corresponds to approx 10 bits being put on the bus at 19200 bps. Except that I can't see the voltage on the TXD pin, everything else is perfect. And I just tried putting a 5K resistor from TXD to ground just to measure. When I do that I can see pulses on the pin but that doesn't help me when coupling to the radio..
ONCE MORE since you did not bother to state the whole derivative names Your question can not be answered based on generic names. Erik