Casio UP-250 Technical Manual page 27

Reception of status from the printer through the bidirectional parallel interface
In bidirectional parallel interface operation, printer status transmission is available using the
two-way communication facility of the IEEE 1284-compatible nibble/byte modes. In this case,
unlike in RS-232 serial interface operation, real-time interruptions from the printer to the host
are disabled, and so you must pay attention to the following.
The maximum capacity of the printer's internal buffer is 100 bytes (except ASB status).
Status signals exceeding this capacity are discarded. To prevent possible loss of status, the
host must be ready for data reception (Reverse Mode).
When ASB is used, the host is preferably in the wait state for data reception (Reverse Idle
Mode). When this state is not available, the host enters Reverse Mode to continually monitor
data presence.
When ASB is used, preference is given to ASB status for transmission over other status
signals. Any accumulated ASB status signals left for transmission from the last to the newest
ASB status transmissions are transmitted together at one time as one ASB status showing the
presence of change, followed by the latest ASB status.
Example: In the normal (wait) state, the ASB status is configured as follows:
In a sequence of operations including near end detection and the paper FEED button being pressed
and released, the following pieces of data are accumulated.
When ASB status is received following this, a total of eight (8) bytes of ASB will be transmitted as follows:
Accumulated ASB ( + + ).
Accumulated ASB (
+
The latest ASB ( )
Fourth Status
First Status Second Status
0001 0000 0000 0000
First Status Second Status
0001 0000 0000 0000
0101 1000 0000 0000
0001 0000 0000 0000
First Status
+ + ) 0101 1000
First Status
0001 0000
Third Status Fourth Status
0000 0000 0000 0000
Third Status Fourth Status
0000 0011 0000 0000
0000 0011 0000 0000
0000 0011 0000 0000
Second Status Third Status
0000 0000 0000 0011
Second Status Third Status
0000 0000 0000 0011
— 18 —
Near end
detection.
Paper FEED
button is
pressed.
Paper FEED
button is
released.
Fourth Status
0000 0000
Fourth Status
0000 0000