DH Instruments PPC2+, Manual

Page: 87 / 166

PPC2+™ Operation and Maintenance Manual
Page 79
©2001 DH Instruments, Inc.
4 . 3 P R O G R A M M I N G F O R M A T S
The PPC2+ program message set is downward compatible with the previous PPC2 program
message set. PPC2+ also introduces a new enhanced program message format to support IEEE Std
488.2 syntax, format, and status reporting. The user must select whether to use either the original
“classic” program message format, or the new “enhanced” program message format. The enhanced
format is recommended when possible, as the classic format is obsolete. Selection can be
accomplished from the front panel (see Section 3.4.4.3) or remotely by using the “MSGFMT”
program message. The default is the classic program message format to allow downward
compatibility with existing host software. The basic commands are similar for both the classic and
enhanced formats, but the usage, syntax, format and status reporting are different.
The PPC2+ enhanced program message format also includes new additional common program
messages that are required in every device that complies with the IEEE Std 488.2. These addition
common program messages are covered separately in Section 4.6.1.
4.3.1 CLASSIC PROGRAM MESSAGE FORMAT
The classic program message format is downward compatible with the previous PPC2
program message set. However, several PPC2 functions are not supported by PPC2 and
neither are their corresponding commands (see DEVICE, DPG, ISO, PPC, HOLD, TOUT,
TS, CONFIG10). This format is recommended only if you need downward compatibility with
older PPC2 controllers. Each program message sent is also a query. You can only send one
program message to the PPC2+ at time. After sending any program message, you must wait
for the PPC2+ to reply before sending another program message. This reply will contain data,
or a numeric error message if the program message was invalid. You must wait for this reply
before issuing another program message to the PPC2+. This insures that the PPC2+
has
completed the program message. Most remote program messages will return a reply within
500 ms except:
PR, PRR, SR, ATM, RATE Up to 2.0 seconds to allow a new measurement.
The syntax and format used for each program message in the classic mode is listed next to
the keyword ‘Classic:’ in each program message summary in Section 4.4.4.
4.3.2 ENHANCED PROGRAM MESSAGE FORMAT
This enhanced program message format uses the IEEE Std. 488.2 format, syntax and status
reporting and is recommended for new applications. Errors are reported using the IEEE Std.
488.2 status reporting model. If an error is reported, the error is put into an Error Queue and
the “ERR?” query program message can be used to get a text description of the most
recent error. If you are using the IEEE-488 port, the service request line can be setup to be
asserted if this occurs (see Section 4.5.2). There are two possible program message types
for every program message. Each of these two types starts with the same basic text referred
to as the program message header.