ISA Bus RS-232/422/485 Communications Card
- Two independent, completely configurable, serial ports
- Supports conventional RS232, High-speed RS-422, and Multi-drop RS-485
- Supports all standard RS-232 lines: TD, RD, RTS, CTS, DCD, DTR, and DI
- Can be wired for 2 or 4 wire RS-422/485 communications
- Supports RS-485 handshaking on-board without special drivers to support Windows and non-DOS programs
- Built-in support for local echo, line termination, and line bias supplies
- Supports extended AT interrupts
- LED status monitors on transmit and receive lines for troubleshooting
The card has type 16550 buffered UART's and is compatible with MS-DOS and multitasking operating systems. I/O bus address is set up by DIP switches on the card and address is not limited to just COMx addresses. Continuous address selection is available anywhere in the I/O address range 100 to 3F8 (hex). Interrupt levels IRQ2 through IRQ14 (except IRQ8, 9, and 13) are supported. A crystal-controlled oscillator is located on the card. This oscillator permits precise selection of baud rate from 50 to 115,000 baud. Higher baud rates are optionally possible using a different UART and higher crystal frequency. The transceiver used, a type 75176, is capable of driving extremely long communication lines at high baud rates. It is capable of driving up to 60 mA on balanced lines and receiving inputs as low as 200 mV differential signal super imposed on common mode noise of maximum -7V to +12V. Also, in case of communication conflict, the transceivers feature thermal shutdown.
In addition to differential Transmit and Receive lines, single-ended, buffered RTS and CTS lines are provided at the I/O connector. Normally, CTS must be pulled up to +5 VDC for the card to operate but you can position a jumper so that the COM-2S will auto-detect the transition between transmit and receive operations. The COM-2S supports full duplex, half duplex and simplex operations selected by jumpers.
RS-485 multidrop communications requires the transmitter drivers to be enabled and disabled as needed to allow the ports to share the common communications lines. The COM-2S card has two methods to control the drivers: automatic (AUTO) and Request to Send (RTS) control. Under automatic control, 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 enabled and remains enabled throughout transmission plus the transmission time of one character after data transfer is complete. Then it is disabled. The COM-2S automatically adjusts its timing to the baud rate of the data. When operating with Windows programs, this AUTO mode is mandatory. With RTS control, your application software must enable/disable the driver.
A transmission line should be terminated at the receiving end in its characteristic impedance in order to eliminate "ringing." You can install jumpers that apply a 120ohm and 0.1 µF capacitive load across the input for RS-422 mode and across the transmit/receive input/output for RS-485 operation. In RS-485 operations, where there are multiple terminals, only the RS-485 ports at each end of the network should have terminating resistors. Also, for RS-485 operation, there must be a bias on the RX+ and RX- lines. If the COM-2S card is to provide that bias, you can install jumpers at the two locations labeled BIAS.
- Tranzorbs to absorb potentially damaging voltage spikes occurring due to lightning or other transmitted electrical interference.
- High-speed crystal oscillators to achieve higher baud rates.
Drivers and Downloads
ACCES also offers Custom Software Services for our products. Our prices are unbelievably low, often as inexpensive as free! If you need something tweaked to support your needs, or an entire enterprise application developed from scratch, it is definitely worth your time to inquire with us, first.
Further information about available ACCES Software:
- Redistributing Windows Drivers
- A list of ACCES drivers and the files that compose them under different versions of Windows, so you can easily redistribute ACCES cards and drivers.
Note: only one serial port shown
- Serial Ports: Two shielded male D-sub 9-pin connectors compatible with RS-232, RS-422 and RS-485 specifications.
- RS-485 Drive: A total of 32 transmitters and receivers allowed on one line.
- Receiver Input Sensitivity: ±200 mV, differential input.
- Input Common Mode Voltage: -7V to +12V.
- Transmitter Output Drive Capability: 60 mA (100 mA short-circuit current capability).
- Serial Data Rates: 50 to 115,200 baud. Asynchronous.
- Address: Continuously mappable within 000 to 3FF (hex) range of AT bus addresses.
- Operating Temperature Range: 0° to +60°C
- Storage Temperature Range: -50°C to +120°C.
- Humidity: 5% to 95%, non-condensing
- +5 VDC: 180 mA, 900 mW.
- +12V: 50 mA, 600 mW.
- -12V: 65 mA, 780 mW.
- 6.5" long. (165 card length)
- Although designed for any AT slot, if installed in an XT-style slot then IRQ10-15 will be unavailable to the card.
- This product is in full compliance with CE requirements.