Rockwell Automation 2755-DM9, -DM9E High Speed Decoder - Manual (Page 117)

Chapter 8
Host Commands Using the RS-485 Interface
8–5
Use the unprotected read command to obtain data from the decoder’s
memory. Using this command you can “map” the memory of the decoder.
The read command is structured as follows:
00000000 00000001
TRANSACTION WORD
HI and LOW ADDRESS BYTES
SIZE OF DATA
MAXIMUM OF
124 BYTES
HI Byte LOW Byte
UNPROTECTED READ COMMAND
Unprotected Read Command Structure
COMMAND (Byte 0) - The command byte for the unprotected read
command has the following structure.
0 0 0 0 0 0 0 1
MSB LSB
0001 =
Unprotected
Read Command
Bit #6 Cleared
For Command
Always Set to 0
STATUS (Byte 1)- Status byte is cleared.
TRANSACTION WORD (Bytes 2 & 3)- As stated earlier, the transaction
word is provided by the host device and returned by the decoder (exactly as it
was sent) in the reply.
Unprotected Read Command