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TimeCritical Message Set
Chapter 9
95
70 — Read Immediate-Access Block
72 — Read Block
73 — Write Bit with Reply
74 — Write Bit with No Reply
75 — Write Block with Reply
76 — Write Block with No Reply
77 — Unprotected Write Byte Command
78 — Unprotected Read Modify Write Command
Each time-critical write is a protected command. That is, if its destination
is a PLC-2 programmable controller, it can only access an area of data
table memory designated by a memory access rung.
STS (Status) — When the command executor receives a time-critical
command, it replaces the CMD field with the STS field to generate the
reply. This one-byte field indicates a successful transaction completion
(00), a link-level error, or a time-critical error. Refer to Appendix A for
link-layer error codes. Time-critical error codes are as follows:
STS Code (Hex)
Description
00
Transaction successfully completed.
B1
Error in destination host.
B2
The specified address does not exist in the destination host.
B3
The address is too close to a boundary for the size of the block
of data specified.
B4
Destination station does not accept memory writes.
B5
Area protected from writes.
B6
Address field invalid or missing.
B7
Missing field.
B8
Reply timeout exceeded.
B9
Command invalid for the destination host mode.
BA
Requested size of block to read is too large.
BB
Total size of fields is too large for write bit command.
BD
The value used in the USER field to specify the immediate
access block is greater than 0F hex.
BE
Invalid CMDfield value.
BF
Size of block to write is too large.
L ADDR (Logical Address) — This field specifies the logical starting
address of the block of memory affected at the destination station which
executes the command. If the destination is a PLC-2 station, this field
specifies a byte address. If the destination is a PLC-3 station, this