I-O Display Systems Basic I/O Product manual Installation, Communication Wiring, 2-6Vol.2

Installation 2

This interaction is heavily dependant on asynchronous timing. Usually, the Host software has no real means of determining that the instruction has been completely sent. This means that the program must calculate the approximate time necessary to transmit the entire instruction before the RS-485 driver is disabled. Since the BASIC I/O AD can respond very quickly to the instruction, the Host must disable the driver as soon as possible in order to receive the BASIC I/O ADs response. RS-485 communications can be tricky at best and should be seriously considered before being adopted. Third party software users should make sure that the package they have chosen supports the particular RS-485 communications card to be used.

Communication Wiring:

The Host to first BASIC I/O AD can be RS-422 or RS-485. Most Host computers come equipped with an RS-232 serial port. A choice must be made to either equip the host with an RS-422 or RS-485 card or to use an external RS-232 to RS-422/ 485 converter such as the duTec BaudMASTER.

For ranges less than 5000 feet, both RS-422 and RS-485 networks can operate in multidrop mode. For ranges greater than 5000 feet, RS-422 (NOT RS-485) networks can operate in repeater mode. In this mode, the distance between individual units can be up to 5000 feet. The trade-off for using the repeat mode is that the powering down of any single unit disables communications with all units further “downstream” from the host.

A network of BASIC I/O AD must be made up of units which are configured as either all multidrop or all repeat.

2-6(Vol.2)