IEEE-488 Reference
3-158
the form of X_ON (^Q) and X_OFF (^S) characters. If the
input queue of the Model 6517A becomes more that 3/4 full
(2048 characters maximum), the instrument issue an X_OFF
command. The control program should respond to this and
stop sending characters until the Model 6517A issues the
X_ON, which it will do once its input buffer has dropped be-
low half-full. The Model 6517A also recognizes X_OFF and
X_ON sent from the controller. An X_OFF will cause the
Model 6517A to stop outputting characters until it sees an
X_ON. Incoming commands are processed after the <LF>
character is received.
Device-Clear Action —
A Control C (°C) sent over the in-
terface interrupts the Model 6517A microprocessor and forc-
es a device-clear action to take place. This clears any pending
operation and discards any pending output. Note that ^X is
also recognized as a device-clear character.
Reception of a break condition also causes a device-clear ac-
tion and displays the appropriate error message (see para-
graph 3.26.3).
The Model 6517A signifies the completion of the device-
clear by echoing back the "DCL" followed by the carriage re-
turn and line feed characters.
Unique SCPI Commands —
The following SCPI com-
mands are unique to the RS-232 interface and cannot be used
over the GPIB interface:
:SYSTem:LOCal
Take the 6517A out of remote
:SYSTem:REMote
Put the 6517A in remote
:SYSTem:LLOCkout <b>
Enable or disable local lockout
See paragraph 3.22.14 for more information on using
these commands.
3.27.3
RS-232 Interface Error Messages
The following error messages are associated with RS-232 in-
terface operation. These error messages are also listed in Ta-
ble 2-5. Note that any of the following errors will set bit B11
of the Operation Condition Register.
+800
"RS-232 Framing error detected" — Start or stop bit
mismatch between computer and Model 6517A.
+801
"RS-232 Parity error detected" — Parity type mis-
match between computer and Model 6517A.
+802
"RS-232 Overrun detected" — Data received before
previous data can be read.
+803
"RS-232 Break detected" — Message indicates that
a Break occurred (device-clear occurs).
+804
"RS-232 Noise detected" — Noisy signals could
corrupt the data.
+805
"Invalid system communication" — RS-232 inter-
face selection lost on power-up. Instrument defaults
to GPIB.
+806
"RS-232 Settings lost" — RS-232 settings lost on
power-up. Instrument defaults to 9600 baud rate, 8
data bits, no parity (none), and 1 stop bit.
+807
"RS-232 OFLO; Characters lost" — A character
was received but discarded due to a lack of input
buffer space. Each line-feed character (<LF>) clos-
es a buffer and opens another. Thus, if too many
line-feeds are sent in succession, then all buffers
will fill before they have a chance to be read.
+808
"ASCII only with RS-232" — You tried to select a
data format (using :FORMat:DATA) other than
ASCII.
3.27.4
Downloading commands using ProComm
There are several communication programs that can be used
to send commands to the Model 6517A. The following sum-
marizes the procedure to use ProComm to download a com-
mand file to the Model 6517A.
1. Using a text editor, type the commands into a file and
save it. An example file is shown as follows:
:syste:pres
:func ‘curr’
:curr:rang 1e6
:syst:zch off
:data:fresh?
2. Go into PCPlus terminal and set the communications
settings to match the settings of Model 6517A (baud
rate, data bits, parity and stop bits).
3. Press the PageUp key on the computer keyboard. PC-
Plus will prompt you to type in a file name. After typing
in the file name, press the Enter key. The command file
will be sent to the Model 6517A.
3.28 DDC programming language
The Model 6517A can be controlled over the GPIB interface
using Device-Dependent Command (DDC) programming. The
DDC programming language is selected from the COMMU-
NICATION item of the MAIN MENU (see paragraph 3.4).
Appendix G lists and summarizes the DDC commands. For
detailed information on Device-Dependent Command pro-
gramming, refer to the Model 617 instruction manual. When
617 DDC mode is selected, the 6517A will power up with
digital filters for all functions disabled, and all NPLCs set to
10. This allows the Model 6517A to accurately mimic the
Model 617’s operation.
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