The Driver

The printer driver should poll the printer port to read the status. If BUSY and BUSY are the same, then there is an error condition (The printer is not connected; it is turned off, or some other major disaster has occurred.), and the hard error flag is set. If BUSY and BUSY are complementary, then the driver checks BUSY and FAULT to see if the printer is busy printing, or if an error condition exists. If BUSY is high and FAULT is high, the printer is busy printing and the driver keeps checking for the printer to become "unbusy" before sending the next character to be printed. If BUSY is high and FAULT is low, then a soft error flag is set. The flow chart is included to give an indication of what happens as the driver checks printer status. It is not an exact representation.

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