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6F2T0207 (0.01)
Figure 11.4-7 Message frame over Data link
Address field of IED device:
The IEDs' identifiers are set by setting [MODBUS_ADDR]. They have to be a
unique number. Each can be selected among 1 - 247.
The [MODBUS_ADDR] has a default setting address (see section 11.4.10).
Function code field:
It is a query/response command code and is transferred over the network. The
features are summarized in Table 11.4-3:
Data field:
It is a container for the query/response command message. The message includes
a content length, inner addresses, status, function responses, etc.
CRC check:
The message is secured by cyclical redundancy check method (CRC). The CRC
value is in 16-bits.
Silent interval
"T1–T2–T3–T4" is a silent one. Figure 11.4-7 shows that it is added at the start
and the end. The silent one is 3.5 character times (at least), and it is multiplied
by the baud rate.
Physical frame (Parity error check)
(iii)
A party error check is added for the RTU frame. It is even parity or odd parity.
The symbols of 1-bit of the RTU frame is counted, and a parity bit (0 or 1) is
generated depending on the counting.
GRE200 (5,6)
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