Black Box PI750A, Руководство пользователя

Страница: 155 / 173

147
APPENDIX D: Sending Direct Commands to the MPS-VIII
/Y and /Z
set exclusive bidirectional link
Use these commands to obtain exclusive bidirectional use of a peripheral.
This is useful when the peripheral returns data to the PC, as do modems and
plotters. An exclusive link approximates having the PC directly connected to
the peripheral, but with an active Multiport Spooler VIII buffer. To establish
an exclusive link, both serial ports must be available when the MPS-VIII
receives the
/Y or /Z command. Otherwise, the MPS-VIII refuses to establish
the link.
You can establish an exclusive link between:
• Two bidirectional serial ports or
• A bidirectional serial port and a serial output port.
In both cases, data can be simultaneously transmitted in both directions.
A /Z bidirectional link is also called a permanent bidirectional link. To
sever the link, you must send a Break signal via the source port.
A
/Y
bidirectional link, also called a
temporary
bidirectional link, is
automatically terminated when the timeout expires (or when you send a
Break signal).
The Multiport Spooler VIII port which receives the command from the PC
is called the “source port” and the MPS-VIII port you want to link to (that is
connected to the desired peripheral) is called the “destination port.” For
some applications you might want to use the MPS-VIII’s configuration
program to set both the source and destination ports to be bidirectional. For
other applications, you might want to set the source port to be bidirectional
and the destination port to be output only. This will depend on the
handshaking protocol the peripherals are using:
1. When the serial port’s flow control is hardware (DTR/CTS):
The exclusive link is established and functions equally well whether both
ports are bidirectional or whether the source port is bidirectional and
the destination port is serial output. In either case, optimum use is
made of the Multiport Spooler VIII’s memory buffer. The DTR and
RTS signals of the source port follow the CTS and DCD signals of the
destination port. The DTR and RTS signals of the destination port
follow the CTS and DCD signals of the source port. If you are using
a fax modem, your communications software will be able to control it
properly; you will also get proper handshaking between external devices
connected to two linked ports.