Comtech EF Data SFC1800A - Manual (Page 43)

SFC1800A Synthesized Frequency Upconverter User Interfaces
TM111 – Rev. 1.0 4-19
4.4 Remote Port User Interfaces
The SFC1800A Upconverter Operator Serial Port allows a remote operator to control the
converter. Through the serial protocols (ASCII and RLLP) described below, the remote operator
can control gain, frequency, calibration, status, and fault isolation. The connector on the rear
panel labeled J8, OPERATOR SERIAL I/O (DB-9 Female) is the physical port used for these
protocols. It can be configured as either a RS-232 or an RS-485 interface. If RS-232 is selected,
an adaptor is needed between the converter connector J8 and the remote controller. See Section
5.9 for detailed pinout information. The port is factory-set to communicate as the DCE (Data
Communications Equipment) with the following settings:
9600 baud
8 data bits
1 start bit
1 stop bit
no parity
The serial protocol is designed to provide DTE-to-DCE Point-to-Point Communications. The
converter is wired as the DCE to provide an interface to a dumb terminal (DTE) without a null
modem connection. Because the serial protocol uses unique addressable commands, the
converters are capable of providing multipoint communications between a number of converters
and a customer-supplied serial interface. The typical multipoint communications configurations
include full-and half-duplex RS-485. In addition, a multipoint RS-232 interface is also possible.
The theory of operation for multipoint requires that the M&C Computer Transmit Port be
connected in parallel to all of the Receive Data Ports of the various converters. Likewise, the
transmit ports of the various converters must all be connected in parallel and tied to the Receive
Data Port of the M&C Computer. To prevent any one Converter Transmit Port from acting as a
low impedance, thus hanging the bus, each transmit port of each converter remains in a high
impedance state until asked by the M&C computer to transmit.
To prevent data collisions from all the converters responding at once, each converter must be
software configured for ‘echo off’ in the Configuration Menu. If the converters are being linked to
a dumb terminal, the echo should be turned on locally.
4.4.1 ASCII Serial Protocol
The ASCII serial protocol serves as a ‘wrapper’ for the M&C data.
4.4.1.1 ASCII Command Structure
This serial command structure uses an ASCII character string format that enables serial control
through the use of a ‘dumb terminal.’ To differentiate a proper command string from noise, all
serial commands have a header followed by the specific command characters, followed by
numeric values where required, and are terminated by a character return . The basic
command structure is as follows:
@{Unit Address/}{Command}{Numerical Value(s)}
For the following examples, a unit address of 01 is assumed.
Refer to Appendix C for Remote ASCII Commends.