19
MODULAR SMART SWITCH
NOTE
The XON/XOFF setting for printer and plotter con-nections is a
bidirectional protocol that recognizes the XON and XOFFcharacters in
both directions. The XON/XOFF setting for com-puter connections
recog-nizes the XON and XOFFcharacters in one direction only. This
allows graphics, font and other non text data to be sent from computers
without problems (the XON and XOFFcharacters 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).
18
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.