I-O Display Systems Basic I/O Product - Manual (Page 24)

Setup & Installation 2
2-7(Vol.1)
approximate time necessary to transmit the entire instruction before the RS-485 driver is
disabled. Since the BASIC I/O can respond very quickly to the instruction, the Host must
disable the driver as soon as possible in order to receive the BASIC I/Os 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 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.
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’s must be made up of units which are configured as either all
multidrop or all repeat.