I have just recently started doing some testing using ignition and a AB micro820. I am trying to pass a USINT via modbus TCP and I cannot get it to work. At the end of the day I want to use USINT to set time values on TOW inputs via ignition. I am able to send an INT and then convert it to USINT, but it'd be nice to not have to use twice as many variables.
It seems strange to me (a modbus illiterate) but the micro820 automatically sets the address in the 0xxxx range (ie a coil) and gives an error if I change it to a 3xxxx or 4xxxx.
Can anyone tell me, if it is possible to read/write a USINT via modbus TCP.??
Thanks in advance for any help, it's starting to get on my nerves.
Modbus doesn't have 8-bit data types. At all. That's why the ML8xx has to use a series of coils.
Your only practical option with IA native drivers, at this time, is to use an INT.
If you are willing to use a 3rd-party module, you have a couple more options:
With Automation Professionals' Advanced Modbus driver, you can address consecutive coils as unsigned integers of various sizes (2 through 63 bits).
With Automation Professionals' EtherNet/IP driver's Generic Client option, you can directly use ML8xx global variables just like the grown-up Logix devices. Browsable, too, with a few restrictions.
{ IA has plans for a native ML8xx driver, but no sign of a release date. }