TransAct POSJET 1500, Руководство программиста

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Programmer's Guide POSjet
®
1500 Port Protocols and
Connection Specifics
Nov-07 Rev M Page 257
Parallel Port Inquire and IEEE 1284
The POSjet
®
1500 Printer supports the IEEE 1284 bi-directional, parallel, peripheral interface standard. The IEEE
1284 standard provides for a bidirectional link on the parallel port. The POSjet
®
1500 Printer only supports Modes
0 and 4, which provide a nibble mode reverse channel for printer identification and status inquire commands. It is
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, 345 East 47th Street, New York, NY 10017, USA.
IEEE 1284 Response Buffer
The POSjet
®
1500 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 POSjet
®
1500 Printer returns:
xx,yy length of following data, 2 bytes with MSB first
MANUFACTURER Ithaca-Periph.
COMMAND SET IPCL
MODEL 1500
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.