On Wed, 4 Jul 2001 07:46:37 +0200 Patrick J writes: > Yes, this was also suggested by Bob Ammerman and it sounds just like > the way > to go for my purpose: 4 sensors connected to 4 PICs so parameters > can be > adjusted aut. by the PC. Actual output from the sensors wont go > through > RS232 since they must be read in sync and responstime is an issue. > > I have also looked into RS485 as Byron refered to in his reply. I am > not sure > how that works, but I found some RS485 tranciver ICs. Speed is > 250kbps > to 4mbps. > > Does 485 use some special protocol, or can I just the TX/RX from the > PIC > to the 485 tranciver ? > PIC1 <-> RS485 tranciver <==== 485 BUS ====> <- RS485 tranciver <-> > PIC2 > The EIA485 transceivers just handle the electrical part of the job. It's your job to figure out a protocol. You have to drive the enable pin on each transmitter at the appropriate time so you don't get contention on the bus. The simplest method is using polling. Have a master unit poll each slave unit. The slaves transmit only when asked. I also use slew rate limited chips (like the MAX488). These help reduce transmission line reflections. You also need to use cable with the appropriate characteristic impedance (typically 110 ohms) and terminate each end of the cable. The Maxim datasheets have lots of good info on this. For short low speed runs, though, I'd just do an "open collector bus." Harold ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: http://dl.www.juno.com/get/tagj. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads