Listening to GPIB Bus Communication - Raspberry Pi

Question

I am making use of Prologix GPIB-USB Controller to be used in LISTEN ONLY mode (Device Mode) to decipher data communication between Two instruments namely Tester & Prober. I have written a sample program in python using Pyserial Module for this purpose.

The issue am facing is that i am able to see the Command and Response communicated between instruments , but cannot listen to the SRQ Signal send over GPIB bus. I am totally new to this area of GPIB programming and have very little knowledge about related stuff.

import os.path
import serial
import sys
from time import sleep

comport = '/dev/ttyUSB0'
# addr = '5'
ser = serial.Serial()

try:
    ser = serial.Serial( comport, 9600, timeout=0.5 )

    # Switch to DEVICE mode
    cmd = '++mode 0'
    print('Sending:', cmd)
    cmd = cmd + '\n'
    ser.write(cmd.encode('UTF-8'))

    # Set instrument to LISTEN ONLY mode
    cmd = '++lon 1'
    print('Sending:', cmd)
    cmd = cmd + '\n'
    ser.write(cmd.encode('UTF-8'))

     # Read the Data from GPIB BUS
    while(True):
        s = ser.read();
        if len(s) > 0:
            print(s)

except(serial.SerialException, e):
    print(e)
    f.close()

except(KeyboardInterrupt, e):
    ser.close()
    f.close()

I am running this code from a Raspberry Pi connected to one end of GPIB-USB Controller and other half connected to GPIB BUS (Connected to both Tester and Prober).

I am able to see all the commands transmitted from Tester and also response for those commands from Prober , But for certain commands the Prober reply back with a SRQ Code , But that is not visible in the Data output collected by this setup.

Output Collected:

F
PN0
?V
PN00453             ,Rzz00-R014.08R,P12,0000000000000000
a
020020
f1
000.0
G
COTBIRD-5S-2CPB-NL  
T (Missing SRQ Reply for this Command)
O
A
A
019021

I am very sure that the SRQ Code is sent after command "T" as i can see the same in Prober Data log generated.

Any guidance would be helpful

Answer 1

The issue was solved by issuing the ++spoll command which reads out the Serial Poll SRQ value requested from the device.