ISA Bus RS-422/485 Communications Cards
The COM422-4 and COM485-4 are communication cards for RS-422 and RS-485 operation respectively. They feature four independent ports, buffered type 16550 UARTs, and automatic control to transparently enable/disable the transmission drivers as needed. There are two connector I/O options. The standard version includes a 25-pin male connector plus a “spider” cable with four DB9 male connectors. Optionally (pictured) two 9-pin male connectors are provided on the card mounting bracket, plus a second mounting bracket with two more 9-pin male connectors and ribbon cable for connections to headers on the card. (To specify this option, add S01 to the model number.)
These cards can receive inputs as low as 200 mV differential superimposed on common mode noise of maximum -7V to +12V. The transmitters feature thermal shutdown.
Continuous address selection is available individually for each port anywhere in the I/O bus address range of 100 to 3F8 (hex) by means of four sets of DIP switches on the cards. Interrupt levels from IRQ2 through IRQ15 (except IRQ 8, 9, and 13) are selectable by means of jumpers on the cards and interrupts are shared. An on-board Interrupt Status Register is included for use when interrupts are shared.
The cards contain a crystal-controlled oscillator and provide precise selection of baud rate from 300 to 115.2k baud. Higher baud rates are optionally possible. If you require baud rates higher than 115.2k baud, give us a call. We may be able to offer what you need at little or no extra cost.
Automatic and Request-to-Send Transceiver Control
Half- and full-duplex communications requires that the transmitter driver be enabled and disabled as needed, particularly in the RS-485 mode where communications lines are shared. These cards have two methods of controlling the driver: automatic (AUTO) for Windows applications and request-to-send (RTS) control. Under AUTO control, the UART is normally in the receive mode. When data is ready to be transmitted, the driver is enabled. The driver remains enabled for the transmission time of one character after data transfer is complete and then the card reverts to receive mode. This AUTO mode allows use of standard Windows RS-232 serial communication drivers in your application.
- High-speed crystal oscillators to achieve higher baud rates.