ACCES I/O PRODUCTS INC. 10623 Roselle St., San Diego CA 92121-1506 Tel (858)550-9559 FAX (858)550-7322 CONV232/422 SERIAL DATA CONVERTER DATA SHEET Model CONV232/422 is a bidirectional RS-232 to RS-422 converter. It converts full-duplex, single ended communication Tx and Rx signals from your RS-232 port to full or half-duplex, differential signal RS-422 operation. Conversion from/to RS-485 both 2-wire and 4-wire are also supported, see details following. FEATURES: • Modes of Operation: RS-422, RS-485 4-wire, RS-485 2-wire • Data Rate: Up to 230K Baud • Low Power Consumption: Port Powered from RTS and DTR lines or External Power, uses all CMOS circuits • Miniature Size Standard DSub 9-pin connectors Connector Pin Assignments J1, RS-232 J2, RS-422 PIN PIN DB9 Female DB9 Male NC 1 Receive- (Rx-) 1 Transmit Out 2 Transmit+ (Tx+) 2 Receive In 3 Transmit- (Tx-) 3 DTR 4 NC 4 Gnd 5 Gnd 5 NC 6 NC6 RTS 7 NC 7 NC 8 Optional External PW R 8 NC 9 Receive+ (Rx+) 9 TABLE 1 OPERATION RS-422 full duplex: The Converter Transmit lines connect to the other RS-422 device receive lines of the same polarity (TX+ to RX+, TX- to RX-) and the Converter Receive lines connect to the other RS- 422 device Transmit lines of the same polarity (RX+ to TX+, RX- to TX-). 1 ACCES I/O Products, Inc. CONV232/422 Data Sheet RS-485 (two wire) half duplex: The Converter transmit and receive lines are connected together at the RS-422 Port Connector by the user (TX+ to RX+, TX- to RX-). The combined lines connect to the other RS-485 device(‘s) lines of the same polarity. The user's software control must enable the RTS signal only during the transmit cycle and then disable RTS to allow the other RS-485 devices to drive the network during transmission. The characters transmitted by the Converter will be echoed to the Converter receiver. RS-485 (four wire) full duplex: When the Converter is plugged into the host Computer, being used as the “MASTER” The Converter transmit lines connect to the SLAVE(‘s) device receive lines of the same polarity. The transmit lines should remain enabled by the RTS signal. The Converter receive lines connect to the SLAVE(‘s) transmit lines of the same polarity. When the Converter is connected at a device that is being used as a “SLAVE” The Converter transmit lines connect to the MASTER device receive lines of the same polarity. The transmit lines must be enabled by the RTS signal only during the transmission from the slave unit and disabled when other slave units are talking The Converter receive lines connect to the MASTER device transmit lines of the same polarity. FIGURE 1, CONNECTION DIAGRAM 2 ACCES I/O Products, Inc. CONV232/422 Data Sheet Termination In order to avoid noise and reflections in long lines, a cable with a characteristic impedance of 120S should be selected and the line should be terminated on both ends with 120S resistors. For short lines (when the propagation of the signal is less than 4% of the time to transmit a bit), the termination might not be needed. This simplifies the network and eliminates the need of external biasing resistors. See NOTE 1 after SPECIFICATIONS for further details. Bias Two 4.7KS biasing resistors on the CONV232/422 RS-422 receive lines are provided to avoid erroneous signal reception when all the transmitters are disabled. Whenever the RS- 422 transmitter is enabled, the driver has full control of the transmission line. When the network is terminated with 120S on both ends of the transmission line and configured with multiple (up to 32) nodes the total bias in the network should be 620S pull up and 620S pull down resistors (or lower resistance for a stronger bias). This is to satisfy the minimum requirement of 200mV of differential signal. Grounding The operation of an RS-422 system requires proper grounding. The presence of a signal reference for both sides of the interconnected equipment is required. An extra conductor in the cable is an easy way to achieve this connection. Alternatively, you could achieve this by connecting the ground pin of each device to earth ground on each end of the network. A 100S ½ W resistance must be added between the earth ground and the signal ground on one side of the network to limit any recirculating currents. FIGURE 2, FUNCTIONAL BLOCK DIAGRAM 3 ACCES I/O Products, Inc. CONV232/422 Data Sheet POWER CONSIDERATIONS The Unit is powered from RS-232 handshake lines RTS and DTR or from an external power source. When powered from the handshake lines, DTR will provide power to the unit and RTS provides both power for the unit, and control for the transmitter. The RS-422 transmitter is enabled only when RTS is high (See Table 2). The RS-422 receiver is always enabled. When the RTS signal is being used to control the RS-422 transmitter, the CONV232/422 can be used as an RS-232 to two wire and four wire RS-485 converter. The CONV232/422 should be powered from external power when the line is terminated with 2x120S resistors and the network is configured with multiple nodes (up to 32). It is important that DTR or RTS be high at all times when external power is not being used. Ensure this in your software if you are not certain your operating system will default the correct way. Control of RTS and DTR DOS, Linux: these signals (RTS & DTR) are both high unless your software specifically exerts a control over them to bring them low. WindowsNT: these signals can be somewhat controlled under “hardware flow control” in the properties tab under the Ports applet. Do not set to “Hardware” flow control. For best results, set to “none”. Windows9x: the signals are controlled under Control Panel, System, Device Manager, Ports, “hardware flow control”. Do not set to “Hardware” flow control. For best results, set to “none”. Converter Power and Control Considerations RTS STATE DTR STATE EXT. POW ER FUNCTIONS (Control and Power line) Low Low Off None Low High Off RS-422/485 RX only High High Off RS-422/485 RX/TX High Low Off RS-422/485 RX/TX High Don’t care On RS-422/485 RX/TX Low Don’t care On RS-422/485 RX only TABLE 2 4 ACCES I/O Products, Inc. CONV232/422 Data Sheet 5 ACCES I/O Products, Inc. CONV232/422 Data Sheet SPECIFICATIONS Optional External Power: +5.5VDC to +16VDC @ 30mA typical to RS-422 Port connector pin 8 with return via J2 pin 5. Data Rate: Up to 230K Baud. Minimum Sensitivity of RS-422 Receiver: 200mV Driver Output Voltage: Unloaded: 4.1V (peak typical) w/50S Load: 2.0V p/p (minimum) Common Mode Voltage, RS-422 Receiver: -7V