HP 800, 700 manual Offset Count, Replacement Count, Control Bit =

HP PCL Commands

Control Bit:	Determines whether the replacement data is encoded, and also the bit
	boundaries of the command byte’s other two fields.
Offset Count:	The number of bytes the replacement data is offset from the current po-
	sition in the seed row.
Replacement	The number of consecutive data bytes to be replaced.
Count:
Control Bit = 0

If the control bit is 0, the replacement data is uncompressed. Bits 0-2 contain the replacement count; bits 3-6 contain the offset count. The replacement count is the number of bytes to be replaced by the bytes following the command byte. The offset count is the location these replacement bytes will occupy relative to the current position in the seed row.

Like compression method 3, the current byte follows the last replacement byte or, at the begin- ning of a row, the left graphics margin. An offset of 0 is the current byte; an offset of 1 is the byte following the current byte.

7	6	3	2	0
Control Bit = 0	Offset Count		Replacement Count

If the offset count is 15, an offset count byte follows the command byte and is added to the command byte’s offset count. If the offset count byte is 0, the offset count is 15. If the offset count byte is 255, another offset count byte follows. The last offset count byte will be less than 255.

One more byte than that indicated by the replacement count will be replaced. That is, 000 = 1 and 111 = 8. For example, if the replacement count is 5, then 6 bytes are replaced.

If the replacement count is 7, a replacement count byte follows the command byte and any off- set count bytes. If the replacement count byte is 0, then 8 bytes are replaced. If the replace- ment count byte is 255, another replacement count byte follows. The last replacement count byte will be less than 255. All of the replacement count bytes are added to the replacement count in the command byte to get the total replacement byte count. One more than the total replacement byte count will be replaced.

Control Bit = 1

Operation is similar if the control bit is 1, except that the replacement data is run length encoded and the bit boundaries are different. Bits 5 and 6 contain the offset count; bits 0 - 4 contain the replacement count. As when the control bit is 0, optional offset bytes and replace- ment bytes may be added.

7	6	5	4	0
Control Bit = 1	Offset Count		Replacement Count

82 HP DeskJet 600, 700, 800, 900 & HP 2000 Series PCL Developer’s Guide