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Chapter 5: Operation
5. Operation
When power is applied to the A/B Switch, one of the LED switch position indicators (A or B) on the front of the unit will
illuminate to show the connection state of the switch. Indicator A lights when the switch is in position A, and Indicator B lights
when the switch is in position B. If neither or both LEDs are lit, then a fault has occurred, or power has been removed.
5.1 Manual Switching
You can manually switch the A/B Switches using the push button switches located on the front of the unit. To select the
connection state, you must hold the appropriate push button switch for one second before the unit will switch. This is to
minimize the risk of inadvertently switching the A/B Switch.
5.2 Dry Contact Closure Switching
You can also switch connection states and monitor the status of the A/B Switch using the remote control connections on the
6-position terminal block, located on the rear of the unit. Connecting (shorting) input A (pin 1) to Ground (pin 2) for a minimum
of approximately 100 msec will cause the unit to switch to the A position, and connecting (shorting) input B (pin 3) to Ground
(pin 2) for a minimum of approximately 100 msec will cause the unit to switch to the B position. If desired, the A or B control
input can remain connected to the Ground input, which will disable all other control interfaces including the front panel
pushbutton switches from being able to switch connection states of the A/B Switch.
NOTE: To ensure reliable operation, the external dry contacts and any associated cable connected to the 6-position terminal block
should not exceed 100 ohms resistance. Once the A/B Switch has switched connection states, the status relay contact pin 5
will be internally connected (shorted) to either pin 4 (switch in position A) or pin 6 (switch in position B). See Table 5-1 for
the pin assignments on the 6-position terminal block.
Table 5-1. 6-position terminal block pin assignments.
Pin Number Description
1
A control input
2
Ground
3
B control input
4
Status Relay A contact
5
Status Relay COMMON
6
Status Relay B contact
5.3 Serial RS-232 Switching (SW1042A-MM, SW1045A-SM)
A/B Switch models that support serial remote control can be switched using commands over a serial RS-232 communications line.
The parameters of the A/B Switch console port are fixed at 9600 baud, no parity, 8 data bits, and 1 stop bit (commonly
abbreviated as 9600, 8, N, 1). To communicate with the A/B Switch, you will need a serial terminal or similar device configured to
these settings. Use a straight-through M/F cable to connect the A/B Switch console connector to this terminal or other device that
follows the standard IBM PC DB9 serial port pinout. See Table 6-1 for the A/B Switch console port connector pin assignments.
When the A/B Switch powers up, it will send a sign-on message followed by a prompt character “>” to your serial terminal
device. After each command and the associated response, the A/B Switch will again issue a prompt character. For systems where
the console port is being commanded by software, the software should wait for this prompt character before sending each and
every command to the A/B Switch. All commands are case insensitive and can be entered in upper or lower case. Note however,
that password parameters are case sensitive. All commands must be terminated with a carriage return (ASCII 13 or hex 0x0D)
before they will be accepted by the A/B Switch. Several commands can be abbreviated by using just the first character of each
command word, for example the set/get system commands can be abbreviated using “g s” for “get system” or “s s a” for “set
system a”.
