Mitsubishi MELSEC-A Series Reference Manual page 44

3. TWO-TIER SYSTEM IN THE MELSECNET/B DATA LINK SYSTEM
(3)
(4)
(5)
REMARK
(1)*1........ When the AnACPU(P21/R21), AnUCPU or A2US(H)CPU(S1) is used,
the LRDP/LWTP/RFRP/RTOP instructions of the dedicated instructions
can also be used.
(For details of the LRDP/LWTP/RFRP/RTOP instructions, refer to the
AnACPU/AnUCPU Programming Manual (Dedicated Instructions) IB-
66251.)
When the QnACPU, Q2AS(H)CPU(S1) is used, the ZNRD/ZNWR/
RFRP/RTOP instructions of the data link instructions can also be used.
(For details of the ZNRD/ZNWR/RFRP/RTOP instructions, refer to the
QCPU (Q Mode)/QnACPU Programming Manual (Common Instructions)
SH-080039.)
Improved RAS (Reliability, Availability, Serviceability) functions
(a) Automatic return function
When a slave station (local station) where an error occurred returns to the link-
enabled state, the station automatically restarts the data link operation. (Refer to
Section 5.3.3.)
(b) Error detection
1) The data link operating state is stored in special relays (M) and special
registers (D) in a programmable controller CPU.
The data link operating state can be checked by reading the data stored in
the special relays (M) and special registers (D).
2) The data link operating state can also be checked by using the link monitor
function at a peripheral device (A6GPP, A6PHP, or A6HGP).
(c) Self-diagnostics function
The self-diagnostics function of the data link module checks the link module
hardware and shielded twisted pair cable connections.
Three operating modes can be selected by setting the CPU module
To satisfy various system configuration requirements, different operating modes can
be selected for the MELSECNET/B data link system by setting link parameters.
The MELSECNET/B data link system has the following three operation modes:
MELSECNET mode, MELSECNET
Section 1.2 gives details about the differences among these modes.
Switching the communication speed is enabled.
The communication speed can be set to 125kbps, 250kbps, 500kbps, or 1Mbps.
The total link distance can be changed by switching the communication speed.
For the relationship between the communication speed and total link distance, refer
to Table 1.1.
mode, and MELSECNET
3 - 4
composite mode.