Hi dear friends, I am using P89LPC936 of philips for my project and i use keil MCB900 evaluationboard. When i test my projects on the MCB900 everything works perfect when sending data trough Rx and Tx pin on the P89LPC936(not after rs-232 tranciever). My GSM phone recives AT-commands perfectly but when i want to use the single chip on a sperate wrapboard using Vdd and Vss only UART does not seem to work properly. The bytes I read from the Rx and Tx seem to be correct but my GSM does not respond to it. I am totally stuck. Tried to change the output mode of the pins but no results. Any clue or help is really appreciated Thank you, Sarsam
"trough a rs-232 datacable connected to my PC the data i send is working good and the phone is responding also correctly." You've been told all this before: A PC COM: port is a proper RS232 port - it includes an RS232 transceiver. You say it works with a PC COM: port. You say it doesn't work direct to your microcontroller with no RS232 transceiver. Surely the answer is obvious - You need to use an RS232 transceiver!