# S7 300 - Error reading S7ReadResponse. Error code = 8304 **URL:** \ **Category:** Ignition\ **Created:** [July 24, 2018, 10:13am UTC](https://forum.inductiveautomation.com/t/s7-300-error-reading-s7readresponse-error-code-8304/18943 "2018-07-24T10:13:48Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![zxcslo](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/zxcslo/32/61610_2.png) [@zxcslo](https://forum.inductiveautomation.com/u/zxcslo)\ **Post date:** [July 24, 2018, 10:13am UTC](https://forum.inductiveautomation.com/t/s7-300-error-reading-s7readresponse-error-code-8304/18943/1 "2018-07-24T10:13:48Z")
I just put the 9th PLC S7 315-2DP on the network an this is what I starting to get in the logs on the Ignition gateway: ![](https://us1.discourse-cdn.com/inductiveautomation/original/2X/d/dcdb86598bb0e82618fa10cb7b46963c72667d03.PNG) What can this mean? ---
**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\ **Post date:** [July 24, 2018, 11:32am UTC](https://forum.inductiveautomation.com/t/s7-300-error-reading-s7readresponse-error-code-8304/18943/2 "2018-07-24T11:32:50Z")
I haven’t seen this error code before. Does it go away if you force a reconnect (edit/save)? Can you check somehow if there are too many connections made to this PLC? ---
**Author:** ![zxcslo](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/zxcslo/32/61610_2.png) [@zxcslo](https://forum.inductiveautomation.com/u/zxcslo)\ **Post date:** [July 24, 2018, 12:10pm UTC](https://forum.inductiveautomation.com/t/s7-300-error-reading-s7readresponse-error-code-8304/18943/3 "2018-07-24T12:10:36Z")
No, it doesn’t go away when edit/save. Also, this PLC has 12 connections available and currently 7 are used:1 for my PG/Laptop, 2 for OP (operating panels) and 4 other… ![](https://us1.discourse-cdn.com/inductiveautomation/original/2X/2/2c142c32fe934e0080fea87b4bf54a5321be66fe.PNG) Also, I noticed that all my tags from this PLC are getting red status for a second and then they come back. ---
**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\ **Post date:** [July 24, 2018, 12:28pm UTC](https://forum.inductiveautomation.com/t/s7-300-error-reading-s7readresponse-error-code-8304/18943/4 "2018-07-24T12:28:38Z")
The best reference to this error I can find is from a Siemens forum post where it's described as: > Error 8304: No further parallel upload possible. Too few resources. Not sure what this means or how to fix it though... maybe one of the other Siemens gurus has seen this before (paging @chi) ---
**Author:** ![zxcslo](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/zxcslo/32/61610_2.png) [@zxcslo](https://forum.inductiveautomation.com/u/zxcslo)\ **Post date:** [July 24, 2018, 12:55pm UTC](https://forum.inductiveautomation.com/t/s7-300-error-reading-s7readresponse-error-code-8304/18943/5 "2018-07-24T12:55:58Z")
I’ve seen that too… I suspect it has something to do with PLC can’t handle all requests… It’s an old PLC, 17-18 years old, with firmware v1.1… ---
**Author:** ![Mike\_Hodgson](https://avatars.discourse-cdn.com/v4/letter/m/47e85d/32.png) [@Mike\_Hodgson](https://forum.inductiveautomation.com/u/Mike_Hodgson)\ **Post date:** [July 24, 2018, 3:51pm UTC](https://forum.inductiveautomation.com/t/s7-300-error-reading-s7readresponse-error-code-8304/18943/6 "2018-07-24T15:51:50Z")
I had this a few years ago and swapped the CPU for the newer slim 315-2DP with MMC and it worked after that. It has 16 communication resources compared to the 12 you have available. Maybe try disconnecting the HMIs or shutting down the S7 software and see if it comes up, that’s how I worked it out. ---
**Author:** ![zxcslo](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/zxcslo/32/61610_2.png) [@zxcslo](https://forum.inductiveautomation.com/u/zxcslo)\ **Post date:** [July 24, 2018, 4:30pm UTC](https://forum.inductiveautomation.com/t/s7-300-error-reading-s7readresponse-error-code-8304/18943/7 "2018-07-24T16:30:13Z")
Yes, that’s my next move too… I have one new CPU (the slim one) and we’ll try to swap the old one. I think (hope) that then it’ll be OK. ---
**Author:** ![chi](https://avatars.discourse-cdn.com/v4/letter/c/0ea827/32.png) [@chi](https://forum.inductiveautomation.com/u/chi)\ **Post date:** [July 24, 2018, 7:54pm UTC](https://forum.inductiveautomation.com/t/s7-300-error-reading-s7readresponse-error-code-8304/18943/8 "2018-07-24T19:54:45Z")
Before changing the processor you may try to increase the reserved ‘OP communication’ ressources, which are used by Ignition’s S7 driver. Of course this may cause problems with the devices that use the ‘other communication’ ressources. Also, 20% cycle load may not be sufficient to handle all communication requests, but increasing this value is dangerous, as it will increase the plc’s cycle time. ---
**Author:** ![zxcslo](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/zxcslo/32/61610_2.png) [@zxcslo](https://forum.inductiveautomation.com/u/zxcslo)\ **Post date:** [July 25, 2018, 5:21am UTC](https://forum.inductiveautomation.com/t/s7-300-error-reading-s7readresponse-error-code-8304/18943/9 "2018-07-25T05:21:09Z")
On my picture, where the connection resources are shown, you can see two connection for OP communications. That’s because I really have 2 OP on the MPI connected to that PLC. When I disable the Ignition S7 driver (device) for that PLC, then the other communication drop to 3. So It seems that Ignition now uses other communications, not OP… I’m also not comfortable with increasing this 20% cycle load, as the plc’s cycle time is already at 30ms… ---
**Author:** ![chi](https://avatars.discourse-cdn.com/v4/letter/c/0ea827/32.png) [@chi](https://forum.inductiveautomation.com/u/chi)\ **Post date:** [July 25, 2018, 9:01am UTC](https://forum.inductiveautomation.com/t/s7-300-error-reading-s7readresponse-error-code-8304/18943/10 "2018-07-25T09:01:58Z")
> [@zxcslo](#): > > When I disable the Ignition S7 driver (device) for that PLC, then the other communication drop to 3.So It seems that Ignition now uses other communications, not OP... Sorry, of course you are right! I confused this with another driver. ---
**Author:** ![zxcslo](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/zxcslo/32/61610_2.png) [@zxcslo](https://forum.inductiveautomation.com/u/zxcslo)\ **Post date:** [July 30, 2018, 3:01pm UTC](https://forum.inductiveautomation.com/t/s7-300-error-reading-s7readresponse-error-code-8304/18943/11 "2018-07-30T15:01:22Z")
Today I swapped the old CPU with the new, slim one with FW 3.3. Now everything is OK. No more errors…✌ I did find a reference to that error 8304 on the Siemens customer support site in the firmware 2.6 update. It seems that from FW 2.6 onward this error does not occur anymore…