Ithaca ITHERM 280, Programmer'S Manual

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beyond the scope of this guide to describe the IEEE 1284 protocol. The complete
specification is available from the Institute of Electrical and Electronic Engineers, Inc. at
www.ieee.org.
IEEE 1284 Response Buffer
The iTherm
®
280 printer has a 256-byte buffer that contains information to be returned
by the IEEE 1284 reverse link. Information is placed in the buffer in the same format as
RS-232 serial information is returned.
Inquire commands sent to the printer in IEEE 1284 mode place responses to the
commands in the IEEE 1284 reverse-channel buffer. The buffer is then transmitted to
the host when it requests the reverse channel.
Mode 4
Mode 4 allows the printer to return identification information to the host system. The
iTherm
®
280 printer returns:
xx,yy length of following data, 2 bytes with MSB first
MANUFACTURER TransAct Technologies
COMMAND SET IPCL
MODEL 1000
COMMENT Rev. x.xx
ACTIVE COMMAND SET IPCL
When a Mode 4 request is made, the IEEE 1284 buffer is cleared before the ID is sent.
Mode 0
Mode 0 provides a reverse channel for information from the printer. Normal responses
to inquire commands are placed in the IEEE 1284 reverse-channel buffer. The Mode 0
reverse-channel request begins returning information to the host. The host may
terminate the transmission at any time. If the link is terminated between nibbles, the last
nibble is retransmitted on the next request. If a complete byte is transmitted, it is deleted
from the IEEE 1284 reverse-channel buffer.
An inquire command can clear the reverse-channel buffer before placing its response in
the buffer.
The IEEE 1284 buffer is limited to 1000 characters. If the buffer is not emptied by
reverse-channel requests, the buffer overflows. The buffer is a first-in first-out (FIFO)
buffer, and the last data placed in the buffer is lost.
Time-outs
IEEE 1284 specifies time-outs for various phases of the protocol. The iTherm
®
280
printer treats time-outs as minimums. The printer time outs at the specified period only if
it is idle during the complete phase.
Active State
The IEEE 1284 reverse channel may be activated at any time as long as the printer is
not busy with data. If the printer is off-line or the cover is open, the reverse channel may