M340 communication problem

hello,

I'm trying out the M340 ethernet messaging mode to communicate with 100 different devices. I'm using a M340 2020 CPU with 2 NOE100, the cpu is HMI dedicated while the NOEs handle the devices.
The results at first are promising, i get very few to no errors at all. After time passes the error count rises and after about 2 hours im getting 100% errors on some of the devices. The errors im recieving are transmission erros (code 7 at read_var parameter register).
Because only 16 connections can be opened when the NOE functions as a client, i'm sending 16 requests at a time (using the READ_VAR function), every time i get a reply (activity bit drops to "0") i switch the IP address and send a new request.
The delay between each read is about 1 second, i've raised that to 5/20 seconds and it doesn't solve the problem.

any advice will be welcomed
thanks

Can you use ioscanner? Two noes should give 128 devices total, if you can get by with fc3, 16, or 23.

By my understanding, although the i/o scanner supports up to 64 devices per module, it only supports 2k registers.
I need 117 registers per device, meaning 11.7k registers.

Yes, that is another limit.

Have you updated the cpu and NOEs to the latest firmware? (available on the Schneider website) CPU firmware should be 2.50 and NOE should be 2.30
when you check the activity, are you checking that all 16 ReadVars are done before starting your next messages?
I would try sending less than the 16 messages at a time, should not need a delay after the activity goes low, so even a couple of simultaneous messages with no delay would probably have a higher throughput than you are currently getting