RS-232 Interface
26
Auto Baud
Auto Baud is used to automatically determine the correct transmission rate. After setting DIP switches 1 through 5,
follow the steps below to use auto baud:
1.
Set DIP switches 6, 7, and 8 to ON.
2.
Connect a controller to the power meter.
3.
Turn the power meter on.
4.
Send the character U (hexadecimal 55) from the controller to the power meter.
5.
Wait 1 second.
6.
If the power meter’s front panel displays LISTEN, the baud rate has been determined. If not, repeat steps 4 and
5.
If, after 30 seconds, the module cannot absolutely determine a baud rate, it will choose a rate based on data
acquired during the test.
Note:
Auto Baud is the only automatically chosen setting. Other items such as parity and stop bits
must be manually selected.
Talker-Only Mode
The Bird 4421 can be set up for manual operation while automatically sending data to an output device (Talker-Only
Mode). To do so, turn DIP switch 2 OFF and cycle the power. TALK will be displayed.
In Talker-Only mode, pressing a button on the meter triggers a measurement. When the measurement is complete,
the information is sent to the bus.
Command Syntax
The Bird 4421 accepts two types of commands. General bus commands are commands, such as Initialize (INT), that
apply to any RS-232 interfaced device. Device-dependent commands are specific to the 4421.
If an invalid command is sent to the unit, an error condition is placed in the serial poll byte and the offending
command is not executed.
A group of device-dependent commands can be sent as a single string as long as like command categories are not
repeated. For example: “PNFCFDT3TRG”. This string sets up the 4421 to send no prefixes, read forward dBm, make
one reading on “TRG”, and triggers a measurement.
Note:
Commands can be entered in either upper or lower case.
Note:
Only the last command entered of each category will be executed. As a command string is pro-
cessed by the 4421, each category of command is stored in a separate location. Two commands of the
same category will be stored in the same location, so that the second will overwrite and erase the first
one.
General Bus Commands
The general bus commands supported by the RS-232 interface module are listed in
Table
14
.
Table 14
RS-232 General Bus Commands
Command
Effect on Bird 4421
INT
Returns to default conditions
ENT
Sends a reading to the controller
TRG
Triggers reading in T3 mode
B1 to B7
Selects a baud rate
XO/XF
Enables/disables software handshake
