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MB_PNHCL function block – Modbus client
Scenario b) At least one response telegram is not received.
Connection 0A
Connection 1A
Server
Client
I/O at modbus block
Request
RECV_TIME
OUT
ENQ = TRUE
Connection
interrupted
Response
DONE = TRUE
ERROR = FALSE
STATUS_0A = 0
STATUS_1A = Error
Request
RECV_TIME
OUT
ENQ = TRUE
DONE = TRUE
ERROR = FALSE
STATUS_0A = 0
STATUS_1A = A0FF
„reuse_conn_
time“ elapses
DONE = FALSE
ERROR = FALSE
STATUS_0A = 0
STATUS_1A = 0
Response
Connection 1A
is recovered
Connection 1A is
internally set to
„available“
Both connections
are used again
Request
RECV_TIME
OUT
ENQ = TRUE
Response
DONE = TRUE
ERROR = FALSE
STATUS_0A = 0
STATUS_1A = 0
SIMATIC Modbus/TCP Redundant Communication of PN H Systems
6AV6676-6MB10-0AX0; Manual Edition 1.1
7-6