Star Micronics 150 manual Print controller using data

Communications PcOS Series 150 Programmer's Guide

Serial Port

The print controller

needs data to print or a command to decode.

Loop through idle task, and then look for more data.

Is there any		Return to print
data in the	No	controller with no data
buffer?		available.

Aquire data from the

buffer.

Move buffer pointers to

the next data byte.

Is the buffer		Set DTR or
below the low	Yes
		transmit XON.
watermark?

No

DTR = Data Terminal Ready

Return data to print

controller.

Figure 23 Print controller using data

The print controller is always looking for data when the printer is on-line and not printing. It continuously asks the buffer if it has any data. If there is no data in the buffer, it does housekeeping chores like keyboard scanning. If there is data, it processes it. The flow control is done when the data is taken from the buffer and the amount of data in the buffer is less than a prescribed amount. This low watermark is set based on the expected environment. The Series 150 Printer sets this at 200 characters, which gives the host application time to get more data to the printer before the printer uses up what it has.

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