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Printek Emulation
Page 7-14
Graphics
Graphics mode gives the user complete control over every dot position on the paper.
Graphics may be printed with various horizontal densities from 60 to 240 dpi, and a
vertical density of 72 dpi.
Each byte of graphics data represents a vertical column of eight dots, with the MSB
(most significant bit) corresponding to the top wire of the print head. Turning a bit on
causes a dot to be printed. The bit values corresponding to each wire of the print head
are shown below:
wire 1 128 (80 hex)
wire 2 64 (40 hex)
wire 3 32 (20 hex)
wire 4 16 (10 hex)
wire 5 8 (08 hex)
wire 6 4 (04 hex)
wire 7 2 (02 hex)
wire 8 1 (01 hex)
The appropriate bit values are added together to fire the desired wires. For example,
a byte of graphics data with the value 128 (80 hex) will fire the top wire, wire 1. A
value of 192 (C0 hex) will fire the top two wires, wires 1 and 2. A value of 11 (0B
hex) will fire wires 5, 7 and 8.
Each graphics sequence contains two bytes (n1 and n2) that specify how many bytes
of graphics data follow. N2 can specify values up to 255. If that is sufficient, then n1
is just set to zero. For values greater than 255, n1 comes into play. The n1 byte
specifies multiples of 256. For example, to specify 520 bytes of graphics data, use n2
= 8 and n1 = 2. The bytes of graphics data are strung together to create a graphics
line that is eight dots high, and (n1 x 256) + n2 dots long. Be sure to provide the
amount of graphics data that you specify, because the printer will not leave graphics
mode until it has accepted the specified number of data bytes.
If "Data Bits: 7" is specified in the "Setup: INTERFACE" menu, beware of potential
problems in graphics mode. Since the MSB (most significant bit) will always be
turned off, it will not be possible to fire the top wire of the print head. Worse yet, the
value of n1 or n2 may be changed. For example, if n1 specifies 200 bytes of data,
and its MSB is turned off, the printer will only expect 72 bytes of data. It will exit
graphics mode, and then try to print the remaining 128 bytes of graphics data as
normal text characters. The result will surely not be pretty. To avoid such problems,
the use of an 8-bit I/O interface for printing graphics is highly recommended.
The normal graphics modes allow every dot to be printed. High speed graphics will
print twice as fast, but will not allow consecutive dots to be printed.