Ithaca PcOS series 90plus, Руководство программиста

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Programmer's Guide PcOS Series 90PLUS Communications
Parallel port
12/16/99 Rev M Page 139
8.2.3.1 Buffer
The Series 90PLUS Printer has a 256-byte buffer that contains information to be returned by the
IEEE 1284 reverse link. Information is placed in this buffer in the same format as RS-232 serial
information is returned.
Inquire commands sent to the printer in IEEE 1284 mode will place responses to the commands in
the IEEE 1284, reverse channel buffer. This buffer is then transmitted to the host when the host
requests the reverse channel.
8.2.3.2 Mode 4
Mode 4 allows the printer to return identification information to the host system. The Series 90PLUS
Printer returns:
xx,yy (length of following data, 2 bytes with msb first)
MANUFACTURER Ithaca-Peripherals
COMMAND SET IPCL
MODEL 90
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.
8.2.3.3 Mode 0
Mode 0 provides a reverse channel for information from the printer.
Normal responses to inquire (ENQ) commands will be placed in the IEEE 1284, reverse channel
buffer. The Mode 0 reverse-channel request will begin returning this 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.
There is an inquire command that will clear the reverse channel buffer. It will clear the buffer before
placing its response in the buffer.
The IEEE 1284 buffer is limited to 256 characters. If the buffer is not emptied by reverse channel
requests, the buffer will overflow. The buffer is a first-in first-out (FIFO) buffer, and the last data
placed in the buffer is lost.
No attempt should be made to send normal data to the printer while the reverse channel is active. Any
data sent to the printer in this mode will be lost and may terminate the reverse channel link.
8.2.3.4 Time outs
IEEE 1284 specifies time outs for various phases of the protocol. The Series 90PLUS Printer treats
these time outs as minimums. The printer will time out at the specified time only if it is idle during
the complete phase.