Modbus read/write request sequencing on PL7

If this is something you do:

What techniques do you use to sequence your modbus read or write requests using the Telemecanique Micro PL7? I trigger the requests by comparing the current value of a timer to a constant, so that every 100ms a different request is triggered. This works great for the most part, but when the quantity of reqests goes up, sometimes there are some errors.

What technique do you use to do this? Do you use the activity reports to sequence the requests?

Don't use PL7, but in the PLC that I use, there is a sequence completion flag, that I use to trigger the next sequence. I should mention, that in the Modbus command, I can have up to 16 seperate messages, on the last application, I had 31 VSD's, with 3 messages to each, resulted in 93 messages, grouped these into 6 sequences of 16 in the protocol file, and once each sequence is completed, enable the next sequence.

Not what your asking I know, but maybe there is a completion flag in the PL7 that you could use, this would more than likely eliminate your errors as well??