Keithley 6482 - Selecting the 488.1 Protocol; Protocol Differences; Message Exchange Protocol (MEP

E-2 Return to Section Topics 6482-901-01 Rev. A / August 2012
Appendix E: GPIB 488.1 Protocol Model 6482 Dual-Channel Picoammeter / Voltage Source Reference Manual
Introduction
The Model 6482 supports two GPIB protocols: SCPI and 488.1. The 488.1 protocol is included to
significantly increase speed over the GPIB.
When using the 488.1 protocol, throughput is enhanced up to 10 times for data sent to the
Model 6482 (command messages) and up to 20 times for data returned by the Model 6482
(response messages). The speed of readings sent over the GPIB is also increased.
NOTE With the 488.1 protocol selected, you will still use SCPI commands to program the
Model 6482. Operation differences between the two protocols are discussed in this
appendix.
Selecting the 488.1 protocol
Perform the following steps to select the 488.1 protocol:
1. Press the MENU key to display the MAIN MENU.
2. Place the cursor on COMMUNICATION, and press the ENTER key to display the
COMMUNICATIONS SETUP menu.
3. Place the cursor on GPIB, and press the ENTER key to display the present GPIB address.
4. Press the ENTER key to display the GPIB PROTOCOL menu.
5. Place the cursor on 488.1, and then press the ENTER key.
6. Use the EXIT key to return to the previous menu.
When switching between the SCPI protocol and 488.1 protocol, the instrument does not reset. The
GPIB protocol setting is saved in EEPROM, and the instrument will power up with that selected
protocol.
The GPIB protocol cannot be changed over the bus. However, there is a query command to
determine the presently selected protocol. When the 488.1 protocol is selected, the message
exchange protocol (MEP) disables. Therefore, if you use the following query to request the state of
MEP, you will know which protocol is enabled:
:SYSTem:MEP[:STATe]?
If a 1 is returned, MEP is enabled, and the SCPI protocol is selected. A 0 indicates that MEP is
disabled, and the 488.1 protocol is enabled. To summarize:
1 = SCPI protocol
0 = 488.1 protocol
Protocol differences
The following information covers the differences between the 488.1 protocol and the SCPI
protocol.
Message exchange protocol (MEP)
When the 488.1 protocol is selected, the MEP is disabled to speed up GPIB operation.
The following guidelines/limitations must be followed when using the 488.1 protocol:
• If a query is sent, it must be the only command on the line (this limitation also means no
multiple queries can be sent). Otherwise, full SCPI command syntax is still supported
including long-form and short form commands, multiple commands, and MIN/MAX/DEF
parameter definitions.