Siemens SIMATIC S7 Manual page 9

Memory
requirements
MODBUS / TCP communication via the integrated PN interface of the CPU
2XV9450-1MB02; Manual edition 2.1
The FB MODBUSPN requires 6048 byte work memory and 7294 byte load
memory.
The FB MOD_CLI requires 11184 byte work memory and 12054 byte load
memory.
The FB MOD_SERV requires 10660 byte work memory and 11452 byte load
memory.
The FB TCP_COMM requires 1880 byte work memory and 2224 byte load
memory.
Product description
1-2