The meter sets the DTR line FALSE in the following cases:
1 When the meter’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 meter sets the DTR line TRUE, unless the second
case (see below) prevents this.
2 When the meter 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 meter, 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 meter sets the DTR line TRUE again, unless the first case (see above)
prevents this.
The meter monitors the DSR line to determine when the controller is
ready to accept data over the interface. The meter 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.
The meter holds the DTR line FALSE while output is suspended. A form
of interface deadlock exists until the controller asserts the DSR line
TRUE to allow the meter to complete the transmission. You break the
interface deadlock by sending the <Ctrl-C> character, which clears the
operation in progress and discards pending output (this is equivalent the
the IEEE-488 device clear action).
Chapter 4 Remote Interface Reference
RS-232 Interface Configuration
180
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