Salter Brecknell CP80 - Manual (Page 5)

CP80 User Guide Page 5 of 11
additional dot line of space each time the motor stops and restarts. In order for this effect to be
avoided the data for each dot line of graphics must be ready and waiting in the printer’s buffer by the
time the previous dot line has been completed.
3.5 DATA
BUFFER
The CP80 has a nominal 8k byte buffer which enables data to be received while previous lines are
being printed. The state of the data buffer is reported to the host by both hardware and software
handshaking.
The hardware busy line is asserted when 512 bytes of space remains; and incoming data are no
longer passed to the buffer when 48 bytes remain. The hardware busy line goes ready again when
528 bytes become free.
The CP80 transmits software handshaking codes when the buffer status changes, as follows:
XON 11H Start transmission
Meaning: The buffer is ready to receive data.
Transmitted after a reset, or when the data buffer empties to only 1/4 full.
XOFF 13H Stop transmission
Meaning: The buffer is not ready to receive data.
Transmitted when the data buffer becomes 3/4 full.
3.6
SERIAL INTERFACE (STANDARD RS-232 VERSION)
The default serial interface format is 9,600 baud, 8 data bits, 1 or 2 stop bits, and no parity. There is
an option of 1200 baud, 8 data bits, 1 or 2 stop bits, and no parity.
Serial data is expected on RxD in RS-232C format with -12V meaning 'mark' or logical '1', and +12V
meaning ‘space’ or logical '0', with reference to the common ground. The serial data output line, TxD,
transmits XON/XOFF to the host at the same baud rate and format as the serial data input. The
hardware busy line, Busy, is true (nominally -12V) when busy.
Some host equipment use a constant space condition (+12V) to indicate a reset condition or wait
state. Some battery powered host equipment present the same output signal when they go to sleep.
By default the CP80will ignore this condition, but this type of host behaviour may result in one or more
spurious characters being received by the CP80.