Step 1: Identify Master Port # and Slave #
The first Load (LD) instruction identifies the
communications port number on the network
master (DL250-1/260) and the address of the
slave station. This instruction can address up to
99 Modbus slaves, or 90 DirectNET slaves. The
format of the word is shown to the right. The
“F1” in the upper byte indicates the use of the
bottom port of the DL250-1/260 PLC, port
number 2. The lower byte contains the slave
address number in BCD (01 to 99).
Step 2: Load Number of Bytes to Transfer
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.
The number of bytes specified also depends on
the type of data you want to obtain. For example, the DL205 Input points can be accessed by
V-memory locations or as X input locations. However, if you only want X0 – X27, you’ll have
to use the X input data type because the V-memory locations can only be accessed in 2-byte
increments. The following table shows the byte ranges for the various types of
DirectLOGIC™. products.
DL205 User Manual, 4th Edition, Rev. B
4–42
Chapter 4: System Design and Configuration
1
2
3
4
5
6
7
8
9
10
11
12
13
14
A
B
C
D
DL205/405 Memory Bits per unit Bytes
V-memory
T / C current value
16
16
2
2
Inputs (X, SP)
8 1
Outputs (Y, C, Stage, T/C bits)
8 1
Scratch Pad Memory
8 1
Diagnostic Status
8 1
DL305 Memory Bits per unit Bytes
Data registers
T / C accumulator
8
16
1
2
I/O, internal relays, shift register bits,
T/C bits, stage bits
1 1
Scratch Pad Memory
8 2
Diagnostic Status(5 word R/W)
16 10
0 1F
CPU bottom port (BCD)
Slave Address (BCD)
LD
KF101
1 2 8
LD
K128
Internal port (hex)
# of bytes to transfer
1
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