Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 125)

7–38 Communication Commands
Publication 1770Ć6.5.16 - October 1996
Important: There are also some limitations on the basic commands
SLC 500 family nodes support:
Command Limitation
Diagnostic Loop Maximum data field size is 95 bytes, not 243.
Unprotected Read
Maximum data field size is 95 bytes, not 244. In addition, the
Addr field is used as a word address instead of a byte address,
and the Size field may contain either an even or odd value.
Unprotected Write
Maximum data field size is 94 bytes, not 244. In addition, the
Addr field is used as a word address instead of a byte address.
When using SLC terminology:
•
The address field in the unprotected read and unprotected write
commands is used as the word offset into the file
•
Thus, to read N9:9 from an SLC 500, put 9 in the address field
(after converting it to 09 hex)
Important: The address fields of unprotected reads and unprotected
writes are used as word addresses instead of the byte
addresses used in the PLC-2, 1774-PLC, and PLC-5
processor. Because of this, existing software drivers
that communicate with the these processors do not work
with SLC 500 family processors, unless you set bit
S:2/8 to a logical one. The SLC 500 processor then
changes to byte addressing mode. This bit is reset to
logical zero by default.
SLC 500 Information
Reading and Writing
SLC 500 Data
Reading and Writing
SLC 500 Data
(using PLCĆ2 terminology)