Active State; Inquire Responses; Parallel Port Inquire (Non-Ieee 1284) - TransAct Ithaca 90PLUS Series Programmer's Manual

Communications
Parallel port
8.2.3.5
The IEEE 1284 reverse channel may be activated at any time as long as the printer is not busy with
data. This means that if the printer is off-line or the cover is open, the reverse channel may be activated.
If the printer is placed back on-line while the reverse channel is active, the printer will not exit the
reverse channel mode.
8.2.3.6
In general, inquire commands place two-byte responses in the IEEE 1284, reverse channel buffer. The
two bytes are the same as the serial mode responses. In IEEE 1284 mode, the printer will remain busy
until the inquire command is processed. This assures responses in real time. To receive the response,
the host must ask for it. It is possible for the host to make a number of requests and wait for the
responses; however, the status returned will be valid at the time the request was made.
It is also possible for the dynamic response mode to be activated and the reverse channel mode to be
opened. The reverse channel will then change from reverse idle to reverse data available as the status
changes. The application must be careful in dynamic response mode that the dynamic responses are not
left active when the reverse channel is closed. If this happens, the output buffer will overflow. If there
is data in the buffer when dynamic responses are activated, it will not be replaced by current status. If
dynamic response is off and a buffer clear command is issued followed by activation of dynamic
responses, the buffer will then contain fresh data. If the buffer clear command is issued after the
dynamic response is activated, the buffer will be cleared and any unread responses will be lost.
8.2.4

Parallel Port Inquire (Non-IEEE 1284)

All inquire (ENQ) commands require some type of 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 ENQ commands is different from serial and parallel, IEEE 1284 modes. In serial and IEEE 1284
operation, inquire commands are responded to by acknowledged (ACK) or not acknowledged (NAK) 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 inquires. If a true paper error is being signaled, the error
(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 rather as a response to an inquire.
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 PE status will
not override any other status request. For example, if you want true PE operation, it must be selected after
all other dynamic status requests.
To synchronize inquire commands with the operation of the PE 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.
Page 134
PcOS Series 90PLUS

Active State

Inquire Responses

Rev Q
Programmer's Guide
11/07/05