Technical FAQs

# How to calculate the max number of X80 HART module in M580 system

There are some limitation of X80 HART configuration in M580 system.
1. MAX 6 HART modules configured with M580 local rack
2. MAX 7 HART modules configured at RIO rack
3. there is still limitation because the memory
The configuration in DTM will impact the memory size of Device DDT of HART module, so there is a calculation

If all variables are enable in the EIP scan:
the input buffer size for AHI = 32(bytes) * 8(channels) + 4 + 8 = 268 bytes, for AHI module.
the input buffer size for AHO = 32(bytes) * 4(channels) + 4 + 4 = 136 bytes, for AHO module.

If four default variables are enable in the EIP scan:
the input buffer size for AHI = 16(bytes) * 8(channels) + 4 + 8 = 140 bytes, for AHI module.
the input buffer size for AHO = 16(bytes) * 4(channels) + 4 + 4 = 72 bytes, for AHO module.

Because the X80-HART modules consume more input memory, so the limitation comes from the input memory capability of the PLC.

If all variables are enable in the EIP scan
In the case of all memory of PLC are used by EIP scan data

l The maximum capacity for AHI module is about
2K  / 268 + 3* (3638/ 268) = 7 + 3*13 = 46 module = 368 device
l The maximum capacity for AHO module is about
2K / 136 + 3* (3638/136) = 15 + 3*26 = 93 module = 372 device

If four default variables are enable in the EIP scan
l The maximum capacity for AHI module is about
2K  / 140 + 3* (3638/ 140) = 14 + 3*25 = 89 module = 712 device
l The maximum capacity for AHO module is about
2K  / 72 + 3* (3638/ 72) = 28 + 3*50 =178 module = 712 device

Note (internal):
The memory fragment is proven to be neglectable to the calculation above.