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Section 3: Interface Specifications
M84Pro Service Manual PN 9001113A Page 3-2
MULTIPLE JOB BUFFER
The printer is able 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. When using the RS232C Serial interface, the multiple job buffer uses either the Ready/
Busy with DTR (pin 20) or X-On/X-Off flow control protocols. See these sections for more details.
With an empty receiving buffer, the status of DTR is “high” (in X-On status if using X-On/X-Off)
meaning the printer is ready to receive data. When the receive buffer is holding 2.0 MB of data (1
MB from being full), DTR will go “low” (an X-Off is sent) indicating the printer can no longer
receive data. This condition is called “Buffer Near Full.”
The receiving buffer will not be able to receive more data again until a “Buffer Available” condition
occurs. This takes place when the receiving buffer has emptied so that only 1 MB bytes of data
are being held (2.0 MB bytes from being full). At this time, DTR will go “high” or an X-On is sent to
tell the host that it can again receive data.
All printer error conditions (i.e., label out, ribbon out) will cause the printer to go busy (DTR “low”
or X-Off) until the problem is corrected and the printer is placed on-line. The printer will also be
busy if taken off-line from the front panel.