Automation Direct D2-DCM, Руководство пользователя

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B–2
RLL Communications Programs
Data Communications Module, 2nd Edition, 2/03
Why are networking instructions needed in your RLL?
Since Direct NET is a master/slave network, the master station must initiate requests for
network data transfers. If you’re using a PLC as the master station, you use simple RLL
instructions to initiate the requests.
Since the D2–DCM network interface does not contain a program, you have to use the PLC to
issue the commands to tell the D2–DCM where to read or write data. The D2–DCM gets
information from the PLC and then converts the information into the appropriate
Direct NET
commands. The RLL instructions use or identify the following items.
1. Uses the special relays assigned to the slot to control the communications.
2. Slot location of the D2–DCM master and the slave station address. (LD instruction)
3. Amount of data (in bytes, decimal) you want to transfer. (LD instruction)
4. Area of memory to be used by the master. (LDA instruction, see the DL205 User
Manual for a detailed memory map.)
5. Area of memory to be used by the slave, and whether it is a read or write operation.
(RX or WX instruction)
6. Interlocks for communication timing and multiple RX and WX routines.
This example reads 3 bytes of data from Slave Address #1,(starting at Y0), into the Master
PLC starting at V40600 (Control Relays).
Master PLC
Slave Address 1
Slave Address 2
Y50
Set SP125
SP124
LD
K201
LD
K3
LDA
O40600
RX
Y0
Communication Error
Communication Not Busy
Example RLL Program
Slave Address D2–DCM Slot
Transfer 3 bytes
Master Starting Address
Slave Starting Address
Type of Operation
Y20 - Y37
15 8 0
Y0 - Y17
Slot 0 CPU Slot 1 Slot 2 Slot 3 Slot 4
The Master Initiates
Requests
Why Ladder Logic?