Communications

PcOS Series 150

Programmer's Guide

Parallel Port

Parallel Port Inquire (Non-IEEE 1284)

All inquire commands require a response from the printer. The serial port is bidirectional; the non-IEEE 1284 parallel port is not. For this reason, the parallel, non-IEEE 1284 operation of inquire commands is different from serial and IEEE 1284 modes. In serial and IEEE 1284 operation, inquire commands are responded to by an acknowledged (ACK) or not acknowleged (NAK) sign and then the command ID on the return link.

In non-IEEE 1284 parallel operation, there is no easy way to return complex information to the host. The paper error (PE) signal is driven in response to inquiries. If a true paper error is being signaled, the ERR line will also be driven. It is, therefore, possible to distinguish between a paper error and an inquire response.

In parallel, non-IEEE 1284 mode, the printer will respond to the inquire before the parallel port sequence is complete. When the parallel port acknowledges the ID portion (the second byte) of the inquire sequence, the PE signal will be valid. The host must, however, remember what status request was made, as the printer has no way of signaling that information. In addition, the host must not interpret the PE signal as an error but as a response to an inquiry.

The PE signal can be configured to respond in two ways. The first is static. The PE will remain valid until the next inquire is issued. It may also be configured to operate dynamically which means the PE signal will follow the status of the feature being tracked. In all cases, a true paper error is dynamic. True paper error status will not override any other status request. For example, if you want true paper error operation, it must be selected after all other dynamic status requests.

To synchronize inquire commands with the operation of the paper error signal, the printer will remain busy after the second byte of an inquire command until the inquire command is processed. This typically takes about 100 microseconds.

P E

 

V a l i d

D A T A

ID

N e xt

S T R O B E

 

 

B U S Y

 

 

A C K

 

 

Figure 19 PE to ENQ request timing

It should be noted that inquire commands are preprocessed (looked at and processed before they are buffered). They are still buffered. This means that the buffer could be filled with inquire commands if the printer is waiting for some other operation.

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Star Micronics 150 manual Parallel Port Inquire Non-IEEE, PE to ENQ request timing