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Chapter 5
RS-232 Interface
This chapter discusses setup of the RS-232 interface feature and describes the RS-232 commands that apply to the
Bird 4421. Operators should understand EIA Standard RS-232-C and have basic computer programming skills before
writing any programs.
Description
The Bird 4421 RS-232 interface feature is an integral part of the I/O hub circuit board inside of the mm21. An eight-
position DIP switch is used to set operational conditions such as baud rate, parity, and stop bits. The bottom line of
the display indicates the current bus status.
Cable Connector
The interface uses a standard 25-pin RS-232 connector. Pin assignments are listed in
Table
13
. If the controller
uses a different wiring arrangement, do not attempt to rewire the interface module’s connector. A null modem kit
should be used for rewiring instead.
Table 13
RS-232
Pin
Assignments
Indicators
The bottom line of the power meter’s display shows indicators describing the status of the Bird 4421 when used
with the RS-232 interface. These are:
TALK —
When TALK is displayed, the power meter is transmitting data. This is always shown when the unit is in
“talker-only” mode.
LISTEN —
When LISTEN is displayed, the power meter is receiving data.
Pin
Designation
Notes
1
Protection Ground
Chassis Ground
2
Transmit Data
3
Receive Data
4
Request to Send
(Output) Set true after module power up
5
Clear to Send
(Input) Set by input device. When true, it enables the
module to transmit. When false, it disables transmission.
6
Data Set Ready
(Input) Set internally true by module
7
Signal Ground
Return path for data and control signals
8
Receive Signal DET
(Input) Set true by module
20
Data Terminal Ready
(Output) Set true after module power up
