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[When the printer driver compression mode is selected]
(1) For the [ESC] SG0; -- command, only “A: Printer driver compression mode” can be selected
for the type of graphic data. The parameter for the data count is attached after the
parameter for the type of graphic data. When the total number of data cannot be provided
by the printer driver, “00H, 00H, 00H, 00H” should be specified for the number of graphic
data. However, in this case, the printer diver cannot support printing through a serial
interface (RS-232C).
(2) How to compress data
Compression is performed for every data of one line specified for the number of graphic
width dots.
The data is made up in units of 8 dots. A repeated value is encoded in 2 bytes. The first
byte is a numeric value n indicating that a value is repeated (-n + 1) times.
The range is between -127 and -1. The second byte is the repeated value.
If a value is not repeated, the first byte is the numeric value m. The length of the values is
indicated in (m+1). The range of “m” is between 0 and 126. The length of the repetition of
the value “n” and ”m” should not exceed 127 and 126, respectively.
If it exceeds the range, it should be divided into blocks of repetition.
When the same contents as the data for 1 line appear repeatedly in the next line and after,
the number of lines in which the same contents appear is encoded in 2 bytes. The first byte
is fixed as 127. The second byte indicates “N” times that the same contents are repeated.
Its range is between 1 and 255. “N” should not exceed 255. If it exceeds the range, the
data for the excess number of times should be compressed as the new data of 1 line, and
the remaining number of repetitions should be encoded.
[Example]
Data before being compressed (Width: 120 dots, Height: 300 lines)
Line No. Graphic data
1 AAh AAh AAh AAh AAh AAh AAh BBh CCh DDh EEh FFh FFh
FFh FFh
2 AAh AAh AAh AAh AAh AAh AAh BBh CCh DDh EEh FFh FFh
FFh FFh
299 AAh AAh AAh AAh AAh AAh AAh BBh CCh DDh EEh FFh FFh
FFh FFh
300 AAh AAh AAh AAh AAh AAh AAh BBh CCh DDh EEh FFh FFh
FFh FFh
Data after being compressed
Line No. Graphic data
1 FAh AAh 03h BBh CCh DDh EEh FEh FFh
2 to 256 7FH FFH
257 FAh AAh
03h BBh CCh DDh EEh FEh FFh
258 to 300 7FH 2BH
FEh = -2
-(-2) + 1 = 3
FFh is repeated 3 times.
03h = 3
3 + 1 = 4
4-byte data (BBh CCh DDh EEh) without
repetition
FAh = -6
-(-6) + 1 = 7
AAh is repeated 7 times.