A single CPU within a network printer executes in multiplex a communication
task for extracting print job data from a packet received from the network
in accordance with the communication protocol, a language task for
interpreting the print job data, and a print task for generating raster
image to be sent to a print engine on the basis of the result of the
interpretation. Further, the CPU includes a watch dog timer (WDT) task
which is activated by the communication task. The WDT task operates in a
manner that, when the communication task is blocked for a long time due to
the busy state of the language task and the print task and can not return
a response to the network, the WDT task returns a response of busy to the
network before the transmission originator disconnects the connection to
the network thereby to maintain the connection, so that a succeeding
packet can be received from the transmission originator when the
communication task is released from the blocked state later.
