# CompactLogix v20 Bad\_CommunicationError **URL:** \ **Category:** Ignition\ **Created:** [May 11, 2017, 6:13pm UTC](https://forum.inductiveautomation.com/t/compactlogix-v20-bad-communicationerror/14266 "2017-05-11T18:13:14Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![readyplayerone](https://avatars.discourse-cdn.com/v4/letter/r/258eb7/32.png) [@readyplayerone](https://forum.inductiveautomation.com/u/readyplayerone)\ **Post date:** [May 11, 2017, 6:13pm UTC](https://forum.inductiveautomation.com/t/compactlogix-v20-bad-communicationerror/14266/1 "2017-05-11T18:13:15Z")
I’m having an issue reading tag values from a CompactLogix using v20 firmware. I can connect to the PLC fine and read all the tag structures. The diagnostics show a connection. Everything looks good, except I cannot read any values form any of the tags. When I try to read a value from the OPC Quick Client I get the following: Read complete Status: Bad\_CommunicationError Value: null Quality: [Bad\_CommunicationError] A low level communication error occurred. Any help would be appreciated. ---
**Author:** ![paul-griffith](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/paul-griffith/32/37249_2.png) [@paul-griffith](https://forum.inductiveautomation.com/u/paul-griffith)\ **Post date:** [May 11, 2017, 6:44pm UTC](https://forum.inductiveautomation.com/t/compactlogix-v20-bad-communicationerror/14266/2 "2017-05-11T18:44:12Z")
What’s the exact firmware version of the device? Although the device drivers short-hand to v21 as the cutoff, some AB devices past a certain v20 revision aren’t fully compatible with our legacy drivers. Try the newer Allen Bradley Logix driver and see if it connects successfully. ---
**Author:** ![readyplayerone](https://avatars.discourse-cdn.com/v4/letter/r/258eb7/32.png) [@readyplayerone](https://forum.inductiveautomation.com/u/readyplayerone)\ **Post date:** [May 11, 2017, 7:26pm UTC](https://forum.inductiveautomation.com/t/compactlogix-v20-bad-communicationerror/14266/3 "2017-05-11T19:26:54Z")
Firmware Version 20.19 ---
**Author:** ![readyplayerone](https://avatars.discourse-cdn.com/v4/letter/r/258eb7/32.png) [@readyplayerone](https://forum.inductiveautomation.com/u/readyplayerone)\ **Post date:** [May 11, 2017, 7:41pm UTC](https://forum.inductiveautomation.com/t/compactlogix-v20-bad-communicationerror/14266/4 "2017-05-11T19:41:20Z")
Using the v21+ driver seemed to solve the problem. ---
**Author:** ![Jesus\_Moncayo](https://avatars.discourse-cdn.com/v4/letter/j/6f9a4e/32.png) [@Jesus\_Moncayo](https://forum.inductiveautomation.com/u/Jesus_Moncayo)\ **Post date:** [February 1, 2023, 1:54pm UTC](https://forum.inductiveautomation.com/t/compactlogix-v20-bad-communicationerror/14266/6 "2023-02-01T13:54:14Z")
I am having the same problem. My customer has firmware version v20.19 and it seems I should stick to this firmware version. Is there a solution for this error? ---
**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\ **Post date:** [February 1, 2023, 2:21pm UTC](https://forum.inductiveautomation.com/t/compactlogix-v20-bad-communicationerror/14266/7 "2023-02-01T14:21:55Z")
You must use the v21+ driver for firmware v20.19, due to Rockwell cutting off the high-performance but totally insecure memory access services that the legacy driver relies on. See this topic: > [@CIP Connection Size Parameter](https://forum.inductiveautomation.com/t/cip-connection-size-parameter/14681/19): > > There’s 2 drivers: the “legacy” driver that works with firmware v20.13ish and prior, and the new “Logix Driver” that works with any firmware version but is optimized for v21+. The new driver is not faster than the old driver. The old driver reads tag values directly out of memory. Rockwell disabled this functionality starting in 20.15? or something like that. In 21+ they introduced a new API for reading tags based on instance IDs (instead of via symbolic names). The new API is certainly faster… ---
**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\ **Post date:** [February 1, 2023, 2:23pm UTC](https://forum.inductiveautomation.com/t/compactlogix-v20-bad-communicationerror/14266/8 "2023-02-01T14:23:29Z")
See also this page in the user manual: [https://docs.inductiveautomation.com/display/DOC81/Allen-Bradley+Ethernet](https://docs.inductiveautomation.com/display/DOC81/Allen-Bradley+Ethernet) ---
**Author:** ![David\_Meherg](https://avatars.discourse-cdn.com/v4/letter/d/ac91a4/32.png) [@David\_Meherg](https://forum.inductiveautomation.com/u/David_Meherg)\ **Post date:** [January 7, 2024, 9:54pm UTC](https://forum.inductiveautomation.com/t/compactlogix-v20-bad-communicationerror/14266/9 "2024-01-07T21:54:59Z")
January 7th 2024. This saved me today. Final day of an outage and after an Ignition version upgrade, this one showed its ugly face! ---
**Author:** ![L\_Grove](https://avatars.discourse-cdn.com/v4/letter/l/b38774/32.png) [@L\_Grove](https://forum.inductiveautomation.com/u/L_Grove)\ **Post date:** [January 28, 2024, 11:39pm UTC](https://forum.inductiveautomation.com/t/compactlogix-v20-bad-communicationerror/14266/10 "2024-01-28T23:39:18Z")
But the firmware version for many 1769-Lxx devices updated to V20.19 maximun. dont have V21. ---
**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\ **Post date:** [January 29, 2024, 3:01am UTC](https://forum.inductiveautomation.com/t/compactlogix-v20-bad-communicationerror/14266/11 "2024-01-29T03:01:53Z")
As noted in the documentation, use the V21 driver for V20.19 firmware. Rockwell backported its closure of the security hole from V21 to the last releases of V20. You must use the V21+ driver for this case. Or flash your devices backwards to ~v20.12, IIRC.