Automation Direct D0-DCM, Руководство пользователя

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MODBUS R
T
U
D0–DCM with
Installation and
5–13
D0–DCM Using MODBUS
DL05/06 Data Communications Module, 1st Edition, 08/05
The second Load (LD) instruction
determines the number of bytes which will
be transferred between the master and
slave in the subsequent WX or RX
instruction. The value to be loaded is in
BCD format (decimal), from 1 to 128
bytes.
1 2 8
(BCD)
# of bytes to transfer
LD
K128
The third instruction in the RX or WX
sequence is a Load Address (LDA)
instruction. Its purpose is to load the
starting address of the memory area to be
transferred. Entered as an octal number,
the LDA instruction converts it to hex and
places the result in the accumulator.
For a WX instruction, the DL05/06 CPU
sends the number of bytes previously
specified from its memory area beginning
at the LDA address specified.
For an RX instruction, the DL05/06 CPU
reads the number of bytes previously
specified from the server, placing the
received data into its memory area
beginning at the LDA address specified.
6 0 0 0
(octal)
LDA
O40600
4
Starting address of
client transfer area
V40600
MSB LSB
0 15
V40601
MSB LSB
0 15
Note: Since V memory words are always 16 bits, you may not always use the whole word.
For example, if you only specify to read 3 bytes, you will only get 24 bits of data. In this case,
only the 8 least significant bits of the last word location will be modified. The remaining 8 bits are
not affected.
The last instruction in our sequence is the
WX or RX instruction itself. Use WX to
write to the server, and RX to read from the
server. All four of our instructions are
shown to the right. In the last instruction,
you must specify the starting address and
a valid data type for the server.
LD
K114
LD
K128
LDA
O40600
RX
V0
SP122
Step 2:
Load Number of
Bytes to Transfer
Step 3:
Specify Master
Memory Area
Step 4:
Specify Slave
Memory Area