COM485-8 is an eight-port asynchronous serial communications card for use in ISA-bus computers. It features eight independent ports, buffered type 16550 UART’s, and automatic control to transparently enable/disable the transmission drivers as needed. Included with the card is a “spider” cable that provides eight shielded, 9-pin, male connectors.
RS-485 multidrop communications under Windows programs requires the transmitter drivers to be enabled and disabled as needed to allow the ports to share common communication lines. The COM485-8 automatically controls the drivers. The port is normally in the receive mode and the driver is enabled only when data is ready to be transmitted. The driver is then automatically enabled and remains enabled throughout the transmission plus the transmission time of one character after data transfer is complete. Then it is disabled. COM485-8 automatically adjusts its timing to the baud rate of the data. This AUTO mode allows use of standard Windows RS-232 serial communication drivers in your application.
The card can accept inputs as low as 200 mV differential superimposed on common mode noise of maximum -7V to +12V. Each transmitter can supply 60 mA current and can drive 32-node, multidrop, two-wire, twisted-pair cable up to 4000 feet long. In case of communication conflict, the transmitters used feature thermal shutdown. Continuous address selection is available individually for each port anywhere in the I/O bus address range 100 to 3FF (hex) by means of eight independent sets of DIP switches on the card. Interrupt levels from IRQ2 through IRQ15 (except IRQ8, 9, and 13) are selectable by means of jumpers on the card and interrupts can be shared. An on-board Interrupt Status Register is included for use when interrupts are shared.
The card contains a crystal-controlled oscillator and provides precise control of baud rate from 300 to 115.2Kbaud. Higher baud rates are optionally possible. If you require baud rates higher than 115.2Kbaud, give us a call. We may be able to offer what you need at little or no extra cost.