Telpar SP-328 Data Logger Thermal Printer
Rev A 8-26-2010
Page 10 of 19
4.3 Flow Control
The SP-328 employs a 31 K byte data buffer to allow the host computer to rapidly transfer data.
Under some circumstances it may be possible to completely fill the buffer. When the buffer is
within 50 bytes of being full, the SP-328 signals the host computer to pause until a line of data is
printed, or until the buffer is under the 50 byte limit The flow control information is sent to the
host using hardware and software protocols.
The hardware protocol uses the BUSY line of the parallel interface and the BUSY line of the
serial interface. These pins are asserted or negated as necessary to turn off and turn on the
flow of data. There is an optional (factory set internal to
the
printer firmware) software protocol
for RS-232 serial which uses the XON and XOFF ASCII characters (^Q and ^S) w
hich
are sent
back to the host to start and stop the data stream. Some host systems may not support one or
both of these protocols.
