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Unit 3: Installation
SATO GT4xxe Series Operator Manual PN 9001138A Page 3-10
RECEIVE BUFFER
The data stream is received from the host to the printer one job at a time. This allows the
software program to maintain control of the job print queue so that it can move a high priority job
in front of ones of lesser importance.
A multiple job buffer allows the printer to continuously receive print jobs while compiling and
printing other jobs at the same time. It acts much like a Print buffer to maximize the performance
of the host and the printer.
The printer receives and prints one job at a time. If a print job exceeds the buffer size,
transmission will be rejected by the printer. Flow control protocols to throttle transmission are not
used. Error conditions that occur during the Print Data transmission will cause the printer to
return a NAK.
ACK/NAK PROTOCOL
Bi-Directional ACK/NAK protocol is used for error control. In a normal transmission sequence
when the transmission is received, the printer will return an ACK (06H) signifying that it was
received without a transmission error. After the transmission command structure has been
analyzed, a status byte is returned to the host. This status byte informs the host of the validity of
the command structure.
If the command structure is error free, the printer proceeds with the print operation. When the
print operation is completed, a Printer Status message is returned to the host. If an error was
detected during the initial transmission sequence, a NAK (15H) will be returned signalling to the
host that the received transmission contained errors and must be resent. If the returned Status
byte indicates a command structure error, the error must then be corrected before the print data
is resent to the printer.
A valid transmission to the printer must be bounded by an STX/ETX pair, with the STX (02H)
signifying the start of the Print Data and ending with an ETX (03H) signifying the end.