17
RS-232 CONTROL
Serial Port:
The 9-pin Sub-D (male) connector on the SPM723 rear panel provides the RS-232 compatible serial interface signals used for
computer control. The SPM723 Serial Port transmits serial data on pin 3 (TxD), receives serial data on pin 2 (RxD), and provides a ground
on Pin 5. The Data Terminal Ready (DTR) & Request To Send (RTS) output signals are connected to the +12 Volt power supply (through
a resistor) and are always asserted when the SPM723 power is on.
NOTE:
The Serial Port may also transmit commands which are
received via the Logic Inputs, depending upon the echo character assignments (see Setup on pg. 9).
pin #1
= not used
pin #2
= Receive Data (RxD) input
pin #3
= Transmit Data (TxD) output
pin #4
= Data Terminal Ready (DTR) output
pin #5
= ground
pin #6
= not used
pin #7
= Request To Send (RTS) output
pin #8
= not used
pin #9
= not used
serial port
5
4
3
2
1
9
8
7
6
The SPM723 only requires receive data (pin 2), transmit data (pin 3), and signal ground (pin 5) to be connected for successful data
communications (see cable diagram below). However, the PC may require that signals be present on the data set ready, clear to send, or
carrier detect inputs, as well as the receive data, transmit data, and signal ground pins. Success or failure depends entirely on the actual
computer hardware and software being used. When trying to solve an interfacing problem, the most important thing to remember is that an
output of one device should connect to one or more inputs of the other device, and that two outputs should never be connected together.
Also, keep in mind that the RS-232 specification calls for the cable length to be no greater than 50 feet (although it is not unusual to be
able to operate over distances of 150 to 250 feet), and the connectors must be of the appropriate gender (male or female) to mate
properly. For best results, a shielded cable should be used, with the shield connected to chassis ground. Since the SPM723 serial
interface ground is also tied (indirectly) to the analog signal ground, undesirable ground loops may occur when the SPM723 is connected
to a PC (if the system grounding is not carefully designed). For best performance, the PC ground and the chassis ground of the SPM723
should be at the same potential, and the PC should get AC power from the same source as the SPM723 (and any other audio equipment
which is connected to the SPM723)
.
Since most lap-top computers are isolated from earth ground, this should rarely pose a problem.
Serial Port Data Communications Parameters:
The SPM723 communicates through the Serial Port at the factory default rate of 38400
bits per second, with 8 data bits, 1 stop bit, and no parity. The SPM723 utilizes a subset of the standard 7-bit ASCII character set. The
eighth data bit of each character (the most significant bit) should always be 0. The computer should not echo the characters it receives.
The computer should not be set for either hardware (DTR) or software (XON/XOFF) flow control. The baud rate may be changed to either
2400, 9600, or 19200 bits per second by means of the software (see Setup on pg. 4).
NOTE:
Baud rate may need to be changed when
the SPM723 is being used in RS-232 systems with other products having a lower maximum baud rate.
Link Port Connections:
The 9-pin Sub-D (female) connector on the SPM723 rear panel provides the RS-232 compatible serial interface
signals used for linking multiple BIAMP
®
products within a system. The Link Port of one device simply connects to the Serial Port of the
next device, and so forth (see diagram below). Link cables are available as an option (Biamp #909-0057-00).
NOTE:
All but the final
device in a system should have its ‘Link’ switch pressed in (see Front & Rear Panel Features on pg. 2). The Link Port may also transmit
commands which are received via the Logic Inputs, depending upon the echo character assignments (see Setup on pg. 9).
pin #1
= not used
pin #2
= Transmit Data (TxD) output
pin #3
= Receive Data (RxD) input
pin #4
= not used
pin #5
= ground
pin #6
= not used
pin #7
= not used
pin #8
= not used
pin #9
= not used
link port
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
CD
RxD
TxD
DTR
DSR
RTS
CTS
RI
gnd
PC
(shield)
serial port
male
female
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
n/a
RxD
TxD
DTR
gnd
n/a
RTS
n/a
n/a
SPM723
serial port
female
male
Serial Cable
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
n/a
TxD
n/a
n/a
n/a
n/a
n/a
gnd
SPM723
(shield)
link port
female
male
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
n/a
RxD
TxD
DTR
gnd
n/a
RTS
n/a
n/a
unit 2
serial port
female
male
Link Cable
RxD
