Seiko FB-900 - Manual (Page 169)

[BUSY]
This signal indicates that the printer is in the busy state.
While it is high, no external data is accepted.
This signal is set to high in any of the following cases:
(1) Initialization is being performed.
(2) The STROBE signal is issued and data is input.
(3) The self-test printing is being performed.
(4) The printer is in the offline state.
(5) The printer cover is open.
(6) The printer is in an error state.
[ACK]
This signal is output at the falling edge of the BUSY
signal which was set high by the STROBE signal. No
ACK signal is output in cases (4), (5), (6) above.
[PE]
This signal is set high when no paper is detected. It is set
low when paper is detected.
[ERROR]
This signal is set low when an out-of-paper error or other
error occurs in the IBM mode.
It is set low when printer is in the offline state, in
addition to the errors noted above, in the EPSON mode.
This signal is set low when the functional error occurs in
the HP mode.
[SELECT]
This signal is always set high in the EPSON mode.
In the IBM mode, it is set low when an out-of-paper
error, paper error or functional error occurs, the printer
cover is opened, the printer is in the offline state, or the
deselect command (ESC + Q + (23)H or (B9)H) is
executed. It is set high when the printer is in the online
state with the ONLINE key or the DC1 (select) command
is executed.
In the HP mode, this signal is set low when the printer is
in the offline state. It is set high when the printer is in
the online state.
● Parallel interface
7-4 — 7. Interface specifications —
Output signals from
the printer
See page 3-53.
See page 6-3.
When #84 ERROR STATUS is set to NO in the
EXTENDED SETUP MODE, PE signal is always set to low
and ERROR and SELECT signals are always set to high.