Black Box SW925A, SW928C, SW929C Setting Serial-Port Protocols and Options, Hardware Handshake

MODULAR SMART SWITCH

NOTE

Automatic detection of the direction of parallel ports is achieved by detecting the state of the SELECT IN signal on the hardware interface. This will operate with most PCs and printers. Automatic detection is not guaranteed to work with all equipment, so if you experience any problems, set the ports as dedicated inputs or outputs.

4.3 Setting Serial-Port Protocols and Options

Protocols

For serial devices, you must set a number of parameters to make sure that the Modular Smart Switch is “speaking the same language” as the equipment that it will communicate with. These parameters include the handshake mode, the baud rate, the parity, the number of bits per character, and the number of stop bits. Most computers and printers are able to set these parameters, so it is generally advisable to set the fastest available. This is often 9600 baud, 8 bits per character, one stop bit, no parity, and either hardware handshake or XON/XOFF.

Hardware Handshake

•DTR/CTS (hardware) handshake uses hardware signal lines to control the flow of data (pins 5 and 20).

Software Handshake

•ETX/ACK—the flow of data is controlled by sending blocks of data and waiting for an ACKnowledgement character to be received.

•XON/XOFF (printer and plotter connections)—the flow of data is controlled by the receiving device by transmitting XOFF (stop data flow) and XON (start data flow) characters. Set this protocol on ports connected to printers and plotters.

•XON/XOFF (computer connections)—the flow of data is controlled by the Modular Smart Switch. This is done by sending XON (start data flow) and XOFF (stop data flow) characters to the computer. Set this protocol on ports connected to computers.

MODULAR SMART SWITCH

NOTE

The XON/XOFF setting for printer and plotter con-nections is a bidirectional protocol that recognizes the XON and XOFF characters in both directions. The XON/XOFF setting for com-puter connections recog-nizes the XON and XOFF characters in one direction only. This allows graphics, font and other non text data to be sent from computers without problems (the XON and XOFF characters often form part of this data).

Ports on the Modular Smart Switch that are set to XON/XOFF handshake will also give the hardware handshake signal to ensure maximum compatibility.

The bidirectional XON/XOFF protocol used for printer and plotter connec- tions can also be used for computer connections if the computer will never send the XON or XOFF characters as part of the data stream.)

RS-232/RS-422 Selection

Each dual serial module supports both RS-232 and RS-422 serial communication. The hardware signals for RS-232 and RS-422 communication appear on different pins of the interface

(see Appendix A for pin-configuration details).

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