Automating Measurements 6-11
Controlling Peripherals
Using the Serial Port
Using the Serial Port
Like the parallel port, the RS-232 serial port can also be accessed using
SCPI and IBASIC commands.
To write a byte with a value of 52 decimal (34 hex, 0011 0100 binary) to
the serial port, use one of the following commands:
OUTPUT @Rfna;"DIAG:PORT:WRITE 9,0,52"
WRITEIO 9,0;52
To read a byte from the serial port, use the following commands:
OUTPUT @Rfna;"DIAG:PORT:READ? 9,0"
ENTER @Rfna;Serial_in
If you are using IBASIC, you can simply use the READIO statement:
Serial_in = READIO(9,0)
For general purpose I/O, the parallel port is much easier to interface to
than the serial port. To interface to the serial port, a Universal
Asynchronous Receiver Transmitter (UART) is typically used to decode
the RS-232 signals. Most UARTs are designed to be used with
microprocessors.
The advantage of the serial port is that it can operate over long
distances: up to 30 meters using the RS-232-C standard. Its
disadvantage is its slow speed which is limited to 19200 bits/second.
Before using the serial port, you must select the baud rate and
handshake style using the SCPI commands:
SYSTem:COMMunicate:SERial:TRANsmit:BAUD
SYSTem:COMMunicate:SERial:TRANsmit:HANDshake {XON|DTR}
One type of application for the serial port is data logging to a remote
computer. After each device is measured, an IBASIC program could use
the WRITEIO command shown above to send a brief summary of the
measurement result, such as a filter's 3 dB bandwidth and its serial
number, to a remote computer. A program on the remote computer would
monitor the serial port and read the incoming data and archive it to a
hard disk or network.
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