SCPI GPIB

Draft version. The following package is designed to be used with the [1] GPIB-Tcl package, to aid the use of GPIB devices that use the Standard Commands for Programmable Instrumentation (SCPI) language [2]. The following code was tested on Windows XP system, with a National Instruments [3] PCI GPIB IEEE-488.2 interface card. The SCPI package was written for a project using three Agilent [4] (was HP) instruments, two 34401A multimeters and a 33220A 20Mhz Function/Arbitrary Waveform Generator. The project is now complete and I no-longer have access to the hardware, so cannot test it on a wider range of instruments. The basic idea was to hide the details of the IEEE SCPI register model from the user. Each SCPI command is wrapped in scpi::cmdSend with commands to clear status and error flags and the OPeration Complete command *OPC, which sets the operation complete flag when all preceding commands are complete. This allows scpi::cmdRead to poll the device for completion, without blocking.

Here is the code:

 # scpi.tcl  --
 #       
 #         This file implements routines built on top of the tcl-gpib
 #         library. It provides a simple interface to IEEE-488.2 
 #         instruments that use the Standard Commands for Programmable
 #         Instruments (SCPI) language.
 # 
 #  $Id: 14780,v 1.12 2005-12-22 07:00:30 jcw Exp $
 # 
 # Change log:
 # $log$
 #
 package require gpib

 #
 package provide scpi 0.1

 # SCPI class of commands
 # Declare namespace.

 namespace eval scpi {
    namespace export *
    
    variable cpoll
    variable data 
 }    

 # scpi::cmd  --
 # 
 # Send (write) a SCPI command to a IEEE-488 instrument
 # Arguments:
 #   id       The id handle for the instrument returned by the gpib open 
 #            command.
 #   message  The SCPI or IEEE command string
 # Results:
 #   code  OK.
 #
 # Example:
 #            scp::cmdSend $id "*rst"  ; # Reset instrument
 #            scp::cmdSend $id "SYST:ERR?" ; # Get error from instr.
 #

 proc scpi::cmdSend { id message } {
     variable data
     gpib clear -device $id
     # Clear status, Set event register, flush OPC
     gpib write -device $id -message "*CLS;*ESE 61;*OPC?"
     set res [ gpib read -device $id ]
     # Write command+OPC.
     gpib write -device $id -message "$message;*OPC"
     set data($id,message) $message
     return -code ok
 } 
 
 # scpi::cmdRead --
 #
 # Perform serialpolls until standard event or time-out.
 # on Time-out: 
 #       Return error with errorInfo.
 # On standard event:
 #    Check for message in message buffer and read.
 #    Check for Error flags in standard event register
 #      if errors read syst:err? into buffer
 #         return error with errorInfo
 #      else
 #         return data if any.
 #
 # Arguments:
 #   id       The id handle for the instrument returned by the gpib open 
 #            command
 # 
 #   ?tlimit? Optional time limit on serialpoll operations.
 #   ?tpoll?  Optional time between serialpoll operations.
 #
 # Results:
 #      Code OK 
 #         Value   data read from instrument if any.
 #      Code ERROR 
 #         Value      null.
 #         errorInfo  Error message and command trace. 

 proc scpi::cmdRead { id {tlimit 2000} {tpoll 100} } {
     variable cpoll 
     variable data
     set cpoll(0) 0
     #  Wait for Standard event OPC
     set time 0
     set cpoll($id) 0
     while { ([set res [gpib serialpoll -device $id]] & 0x20 ) != 0x20 } {
         # puts "Poll: $res"
         if { $time < $tlimit} {        
             # after $tpoll
             after $tpoll [list incr ::scpi::cpoll($id) ]
             if {![info exists tk_version] } {
                 vwait ::scpi::cpoll($id)
              } else {
                  tkwait variable ::scpi::cpoll($id)
             }
             incr time $tpoll
         } else {
             set result "Time-out after ${tlimit}ms waiting for Standard Event \
 (Operation complete or Error)"
             return -code error -errorinfo $result 
         }
     }
     # Check Message AVailable (MAV) and read Message buffer        
     set result {}
     while { ([set res [gpib serialpoll -device $id]] & 0x10 ) == 0x10 } {
         lappend result [ gpib read ]
     }
     # Check event register
     gpib write -device $id -message "*ESR?"
     set sevent [ gpib read -device $id ]
     # Check for error bits in Standard event register
     #
     if { ( $sevent & 60 ) != 0 } {
          lappend result $sevent
         # Get system error
         gpib write -device $id -message "SYST:ERR?"
         set serror [ gpib read -device $id ]
         lappend result  $data($id,message) $serror
         return -code error -errorinfo $result 
     }
     return -code ok $result
 }

 # scpi::cmd --
 #      
 #      Combines scpi::cmdSend and scpicmdRead in one call.
 # 
 # Arguments:
 #   id       The id handle for the instrument returned by the gpib open 
 #            command.
 #   message  The SCPI or IEEE command string
 # 
 #   ?tlimit? Optional time limit on serialpoll operations.
 #   ?tpoll?  Optional time between serialpoll operations.
 #  
 # Results:
 #      Code OK 
 #         Value   data read from instrument if any.
 #      Code ERROR 
 #         Value      null.
 #         errorInfo  Error message and command trace.
 
 proc scpi::cmd { id message {tlimit 2000} {tpoll 100} } {
     cmdSend $id $message 
     cmdRead $id $tlimit $tpoll
 }


 # scpi::cmdList --
 #
 #      Execute a list of scpi commands on an instrument.
 #
 # Arguments:
 #   id       The id handle for the instrument returned by the gpib open 
 #            command.
 #   mlist    A Tcl list of SCPI commands 
 #
 #   ?tlimit? Optional time limit on serialpoll operations.
 #   ?tpoll?  Optional time between serialpoll operations.
 # Results:
 #      Code OK 
 #         Value   list of data read from instrument if any.
 #      Code ERROR 
 #         Value      null.
 #         errorInfo  Error message and command trace.

 proc scpi::cmdList { id lmess {tlimit 2000} {tpoll 100} } {
     global errorInfo
     set result {}
     foreach Cmd $lmess {
         if {[catch {cmd $id $Cmd $tlimit $tpoll} val ] != 0} {
             set saveInfo  $errorInfo
             error {}  $saveInfo
             return -code error
         } else {
             lappend result $val
         }
     }
     return -code ok $result
 }



Simple example of usage:-
 package require gpib
 package require scpi
 # open the GPIB device
 set dvm1 [gpib open -address 22 -sendeoi true ]
 # Request a measurement from the DVM. 
 # Wait upto 2 seconds and poll for completion every 200ms.
 scpi::cmd $dvm1 "meas?" 2000 200
 # List of commands to configure DVM.
 set instrument(dvm1,conf) [list "*RST" \
                               "*CLS" \
                               "CONF:VOLT:AC DEF,DEF " \
                               "DET:BAND 3" \
                               "TRIG:SOUR IMM"] ;
 # execute list of commands.
 scpi::cmdList $dvm1 $instrument(dvm1,conf)
 more to add here, async usage.
 # close device
 gpib close -device $dvm1

Category Device Control