Ap890 and Ap892 User Guide Page 4 of 12
2.5
DOT ADDRESSABLE GRAPHICS
Graphics patterns are built up as a succession of complete dot lines across the paper, rather like a TV
picture. Complete dot lines must be specified at a time. The data for each dot line of graphics should
be encoded as shown:
For the Ap890:
ESC, 01H, d
1
…d
24
(a total of 26 bytes per dot line)
For the Ap892:
ESC, 01H, d
1
…d
40
(a total of 42 bytes per dot line)
Bits 5 through 0 of each data byte (d
1
through d
24
or d
40
) are interpreted as encoding individual dots
on the paper, where 1 represents a dot, and 0 represents a space. Bits 7 and 6 are ignored.
Large areas of solid dots are not recommended, as they may cause overheating and shorten the
ribbon life: try shading. Heavy graphics printing will also drain the battery more quickly.
N.B.
If multiple dot lines of graphics are required to be contiguous, care must be taken to ensure that
the data rate is high enough to allow continuous printing. This is because the mechanism inserts an
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.
2.6
DATA BUFFER
The Ap890 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 Ap890 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.
N.B.
An XON character is transmitted when the printer has woken up and is ready to receive data, but
no XOFF character is transmitted prior to the Ap890 entering sleep mode.
2.7
SERIAL INTERFACE
The default serial interface format is 9,600 baud, 8 data bits, 1 or 2 stop bits, and no parity. Other
formats can be programmed into the Ap890 at the factory.
Serial data is expected on Rx 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, Tx,
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. Both serial output lines will relax to
approximately 0V when the Ap890 is in sleep mode, and the user must allow a short period after
awakening before relying on the values of these signals.
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 Ap890 will ignore this condition, but this type of host behaviour may result in one or
more spurious characters being received by the Ap890, or the Ap890 may be prevented from going to
sleep.
