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to the serial interface and are not displayed when you select the parallel
interface.
When you select the serial interface, you must also select certain other
values in the INTERFACE menu in order to match the features of the host
computer. The additional features are described next.
4.5.6.2 Baud Rate (baud)
The baud rate (baud) feature sets the transmit and receive speed the printer
uses to communicate with the host computer. The printer speed must match
the speed used by the host computer.
4.5.6.3 RS232C Data Format (rsmode)
The RS232C data format (rsmode) feature determines the data format the
printer uses to communicate with the host computer. The first part of the
value (7 or 8) is the number of data bits the printer expects to see in each
character it receives. The second part of the value is the type of parity
(checking) bit the printer looks for in each character. A parity check is a
method used to detect errors when data is sent over a communications line.
Some systems use an odd parity bit to detect errors, while other systems
use an even parity bit. Some systems use no parity bit at all. The third
part of rsmode is the number of stop bits. Some systems use one stop bit
while other systems require two. The format for the data bits, parity bit,
and stop bits must match the format of the host computer in order for the
printer and the host to communicate.
4.5.6.4 Data Terminal Ready (dtr)
The data terminal ready (dtr) feature uses hardware to regulate the flow
of data to the input buffer of the printer. Regulation is accomplished by
toggling a signal on the DTR line of the serial port when the printer is ready
to receive data. This is sometimes referred to as hardware handshaking
protocol.
For Digital systems, the dtr feature should always be set to the fixed high
value. When the DTR signal is fixed high (Fix-H) it indicates to the system
that the printer is ‘‘present.’’
4.5.6.5 Buffer Control (xon/xoff)
The buffer control (xon/xoff) feature uses software to regulate the flow of
data to the input buffer of the printer. It is sometimes referred to as
software handshaking protocol, a method the printer and the host computer
use to exchange on/off signals. These signals prevent the input buffer from
overflowing with data. If the input buffer becomes full and handshaking is
not enabled, the overflowing data will be lost. Xon/xoff must be enabled in
systems that use this software handshaking protocol to prevent the loss of
data.
Printer Configuration 4–29