| ??? 09/22/09 11:50 Read: times |
#169041 - Which lesson to give? Responding to: ???'s previous message |
Per Westermark said:
And what do you think happens with the signals, when you connect two transmitters together? Don't you think the PC will have a hard time hearing any messages sent from one of the two 8051 chips?
You are not expected to do it, but you can connect multiple listeners to an RS232 cable. And you can obviously connect the logic-level signal from a MAX232 chip to multiple receivers. But you need special designs to allow multiple transmitters. Some serial designs are using tri-state and some are using open-collector drive, to allow multiple masters on a wire. RS232 is designed for one master in each direction. Andy Neil said:
Tony Gelonese said:
Parallel the 2 TX lines of the 8051's together No, as Per says, that will not work - at least, not without some special hardware and software design to ensure that the two 8051s cannot both transmit at the same time! It works, end of story. 'fraid not - it can be made to work, but there is a lot more to the story! Gentlemen, I do not have the time or inclination to give lessons in either English or the I/O structure of a typical 8051. Read my post carefully. I have 3 Atmel 2051 micros with serial I/O's connected in parallel, communicating with a PC through 1 serial port only. This has been in industry for over 5 years and working very well. The PC issues a command which all 3 micros listen to. Only the one which was addressed will then execute the command and respond. Like good little children the others wait till they are spoken to before they respond. The circuit is simplicity itself. Cheers, Tony :) |
