Appendix A: D50 PLC Communication Protocol 161
Read Bits
The following can be read:
• Bits stored in the absolute address (R, L, M, K, or F).
• N consecutive bit contents (On/Off).
Query (Q) frame
Response (R) Frame
Number of bits to be read
bsolute bit address
(address of first bit to read)
For example:
K12.12 (address K12’s 12th bit)
Absolute bit address = $14CC
Length of
information
bit
Function Code
Peripheral Device
ID
PC ID
PLC ID (CPU ID)
Base CRC
DA SA $01 $03 L H N L H
Bits that are On are represented by the
one byte value $FF. Bits that are Off have
a value of
00.
Length of information (number of bytes)
from the len
th to the next CRC.
Response code ($80 added to the
original function code).
PLC ID (CPU ID)
Peri
heral Device ID
PC ID
For the response, the PLC is the sender
and the PC the receiver, so the DA and SA
are reversed from the Q message.
DA SA $81 N Bit value Bit value … Bit value L C
Base+0 Base+1 Base+N-1 CRC
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