| 摘要 |
PURPOSE:To enable a multiplicity of pieces of data to be outputted, without complicating a circuit construction through an increase in the number of I/O elements or the like, by a method wherein an I/O port for inputting data from the side of a host system is used as an output port. CONSTITUTION:A printer-controlling circuit 60 comprises a microcomputer 61, a latch circuit 62 in which output terminals OUT can be controlled to a high impedance by an external signal and which constitutes a port-switching means, AND circuits 63-67 by which turning-ON signals for indicators are made to be valid or invalid in accordance with the mode of an I/O port A of the microcomuter 61, etc. In accordance with the results of error discrimination, the microcomputer 61 causes a signal for controlling the output terminals OUT of the circuit 62 to a high impedance to be outputted from a port P0 of the I/O port B, whereby ports P0-Pn of the I/O port A are switched to output ports, and error data are outputted through the output ports P0-Pn. |
