Keysight E3633A, User Manual

Page: 88 / 205

3 Front-Panel Operation
88 Keysight E3633A and E3634A User’s Guide
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.
The power supply monitors the DSR line to determine when the bus controller
is ready to accept data over the interface. The power supply 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 power supply holds the DTR line FALSE while output is suspended. A form of
interface deadlock exists until the bus controller asserts the DSR line TRUE to
allow the power supply to complete the transmission. You can break the interface
deadlock by sending the < Ctrl-C > character, which clears the operation in
progress and discards pending output (this is equivalent to the IEEE-488 device
clear action).
For the <Ctrl-C> character to be recognized reliably by the power supply while it
holds DTR FALSE, the bus controller must first set DSR FALSE.