DTR / DSR Handshake Protocol
The multimeter is configured as a DTE (Data Terminal Equipment) device
and uses the
DTR (Data Terminal Ready) and DSR (Data Set Ready) lines
of the
RS-232 interface to handshake. The multimeter uses the DTR line
to send a hold-off signal. The
DTR line must be TRUE before the
multimeter will accept data from the interface. When the multimeter
sets the
DTR line FALSE, the data must cease within 10 characters.
To disable the
DTR/DSR handshake, do not connect the DTR line and tie
the
DSR line to logic TRUE. If you disable the DTR/DSR handshake,
also select a slower baud rate (300, 600, or 1200 baud) to ensure that
the data is transmitted correctly.
The multimeter sets the DTR line FALSE in the following cases:
1 When the multimeter’s input buffer is full (when approximately
100 characters have been received), it sets the
DTR line FALSE (pin 4 on
the
RS-232 connector). When enough characters have been removed to
make space in the input buffer, the multimeter sets the
DTR line TRUE,
unless the second case (see below) prevents this.
2 When the multimeter wants to “talk” over the interface (which means
that it has processed a query) and has received a <new line> message
terminator, it will set the
DTR line FALSE. This implies that once a
query has been sent to the multimeter, the controller should read the
response before attempting to send more data. It also means that a
<new line> must terminate the command string. After the response has
been output, the multimeter sets the
DTR line TRUE again, unless the
first case (see above) prevents this.
The multimeter monitors the
DSR line to determine when the controller
is ready to accept data over the interface. The multimeter monitors the
DSR line (pin 6 on the RS-232 connector) before each character is sent.
The output is suspended if the
DSR line is FALSE. When the DSR line
goes
TRUE, transmission will resume.
4
Chapter 4 Remote Interface Reference
RS-232 Interface Configuration
151
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