Trouble with serial port work.

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..

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  • 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.

    That's what you get for using Atmel :)

    Seriously: since you state "33 MHz one" did you change the crystal.

    another possibility, since you did not bother to state the whole derivative name (all Philips chips have a 'P') it could be that one was an x2 and the other not. or that one was programmed as an x2 and the other not because the (default and?) programming is different.

    a third possibility, since you did not bother to state the whole derivative name is that one chip has configurable pins .

    a fourth possibility, since you did not bother to state the whole derivative name is that the UART activation differ.

    Erik

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  • 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.

    That's what you get for using Atmel :)

    Seriously: since you state "33 MHz one" did you change the crystal.

    another possibility, since you did not bother to state the whole derivative name (all Philips chips have a 'P') it could be that one was an x2 and the other not. or that one was programmed as an x2 and the other not because the (default and?) programming is different.

    a third possibility, since you did not bother to state the whole derivative name is that one chip has configurable pins .

    a fourth possibility, since you did not bother to state the whole derivative name is that the UART activation differ.

    Erik

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