Dtr/dsr handshake protocol – Agilent Technologies 34401A User Manual

Page 157

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

-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

-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

-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.

Chapter 4 Remote Interface Reference
RS-232 Interface Configuration

151