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Chapter 3 Front-Panel Operation
RS-232 Interface Configuration
66
DB-25 Serial Connection If your computer or terminal has a 25-pin serial
port with a male connector, use the null-modem cable and 25-pin adapter
included with the Agilent 34398A Cable Kit. The cable and adapter pin
diagram are shown below.
DTR / DSR Handshake Protocol
The power supply 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 power supply uses the DTR line to send
a hold-off signal. The DTR line must be TRUE before the power supply will
accept data from the interface. When the power supply 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 to ensure that the data is transmitted correctly.
The power supply sets the DTR line FALSE in the following two cases:
1 When the power supply’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 power supply sets the DTR line TRUE, unless the
second case (see next) prevents this.
2 When the power supply 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 power supply, the bus 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 power supply sets
the DTR line TRUE again, unless the first case (see above) prevents this.