Modbus/ModBus Plus Requests Per MAST Task Scan

Maximum Request Served

The maximum number of requests served depends on limitations at various levels:

Module port limitation: The number of requests served depends on the module port capacity to serve those requests.
CPU architecture limitation: The number of requests served depends on the CPU capacity to send and treat those requests through the PAC architecture.
CPU com server limitation: Parameter set to define the maximum number of requests to be served.

The maximum number of requests is determined by the most restrictive limitation.

Modbus/Modbus Plus Server Mode Communication

The following table provides the maximum number of served requests per MAST task scan for a Modicon Quantum Modbus or Modbus Plus communication in server mode:

Priority (Service Order)	Requests Entry Port	Maximum Number of Requests
Priority (Service Order)	Requests Entry Port	Module Port Limitation	CPU Architecture Limitation	CPU Com Server Limitation
1	Requests via a CPU embedded Modbus or Modbus Plus port.	4	20	4...24 Set with %SW90
2	Requests via NOM module.	4
2	Requests via NOE or NOC module in 4 x 256 communication mode.	4 (1)
3	Requests via NOE or NOC module that support n x 1024 communication mode, with n depending on module (n x 1024 bytes is selected). NOTE: Available for NOE with SV≥4.60.	n = 4, 8, or 12 (1)	12 (high-end CPU) 8 (legacy CPU)
4	Requests via USB port.	4	No limitation
5	Requests via embedded Ethernet ports.	16	No limitation
(1) Limitation applies to other requests than FC03, FC16, or FC23 which are directly served by the module. In addition to the maximum requests per module, up to 8 requests of type FC03, FC16, or FC23 can be served per scan per module.

Example for requests via embedded Ethernet port: Limitation 1: Module port limitation to serve requests via embedded Ethernet port = 16 Limitation 2: CPU setting: %SW90 = 4 Result: Maximum number of served requests = 4.

In this case, the most restrictive limitation comes from the CPU setting.