ZETRON Model 25, Руководство по эксплуатации продукта, Страница: 137 / 147

Index
025-9567E 129
APPENDIX C - INTERFACING MODEL 25 TO CAD SYSTEMS
The Zetron Model 25 Programmable Encoder is easily controlled by a computer for
computer aided dispatch (CAD) applications. The purpose of this application note is to
describe the computer-to-encoder interface and communications protocol. At the end, you
will also find the electrical specifications of the computer port on the Model 25. The features
described here are only available on Model 25s equipped with version 1.20 or later software.
Computer-to-Encoder Interface
The encoder interface to the computer is the computer port connector. This nine-pin socket
can either be mounted on the front or rear panel. Complete computer control of the encoder is
possible via this connector. Four important RS-232C compatible signals are available at this
connector; transmit data (
TX-DATA
), receive data (
RX-DATA
), remote control (
RMT-CTL
)
and signal
GROUND
.
TX-DATA
is the RS-232 output from the encoder which provides information to a computer
about call progress.
RX-DATA
is the RS-232 input to the encoder used by a computer to
control the encoder. One second or more of a continuous
space
level on the
RX-DATA
signal will cause the encoder to reset thus halting any radio transmissions in progress (a long
space
level on the
RX-DATA
signal is commonly known as a
break
). The
RMT-CTL
signal
is used to alter the mode of operation for the encoder. The two operating modes are the
instant call mode and remote control mode. A
mark
level on the
RMT-CTL
signal configures
the encoder in the instant call mode thus enabling the instant call keys but disabling control
via computer. When in instant call mode, the
RX-DATA
signal must not receive any
characters from the controlling computer, otherwise an error may occur. A
space
level on
the
RMT-CTL
signal configures the encoder in the remote control mode thus enabling control
via computer but disabling the instant call keys. In either operating mode, the encoder keypad
section, on the left side of the front panel, can be active.
While the encoder is idle, the operating mode can be switched by changing the level of the
RMT-CTL
signal and pausing two seconds for the new operating mode to take effect. A
change of level on the
RMT-CTL
signal will not be noticed by the encoder until it is idle (not
transmitting). The idle state can be brought about by resetting the encoder via a
break
(described above), and pausing for two seconds. Resetting the encoder, however, will cause
calls in progress to be terminated and any pending instant calls to be cleared. When the
encoder detects a change in the
RMT-CTL
level, the equivalent of a reset also occurs.
Table 30 and Figure 16 show two suggested interface wiring options. The Computer Priority
option gives the computer full control of mode selection. The Operator Priority option gives
the operator control of the mode selection via a toggle switch.