Specifications

69
Schneider Electric
The Modbus Protocol (continued)
Read trace buffer: function 12
Note: Functions 12, 13 and 14 are not implemented in all Modicon controllers and
are given only for information because they are on the list of Jbus functions.
The master can request a read operation on this memory. The slave responds, and
sends the contents of the event counters and message counter as well.
b Query.
b Response.
b In reception.
b In transmission, error number if any.
b In disconnected mode (1).
b Diagnostic counters reset to zero (command 8, sub-command 01).
(1) Disconnected mode is used to analyse certain problems. In this mode, the
coupler monitors the line and increments counters and updates the trace table.
However there are no transfers to the slave’s memory and no responses are
transmitted on the line. This mode is piloted by command 8 (sub-functions 01 and
04).
The user can access a 64-byte memory
containing the history of the last 64
transactions.
E52376E52377E52378E52379E52380E52381
Slave No. 0C CRC 16
1
byte 1 byte 2 bytes
Slave No.
OC
46 00 00
CRC
1
byte 1 byte 1 byte 2 bytes
Status of
event counter
2 bytes 2 bytes
Status of
message
counter
Report on most
recent event
Report on event
immediately
preceding
Report on
event N
Report on
event -64
64 bytes
1
= 1 if
broadcast
= 1 if
disconnected
mode
= 1 if CRC
error
1 if erroneous
character
0
0
0
1
1
= 1 if
disconnected
mode
0
0
0
1
0
0
0
00
0
0
0
0
0
0
00
Guide to Integration
Modbus / Jbus