Automation Direct D2-DCM, Руководство пользователя

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B–5
B–5
RLL Communications Programs
Data Communications Module, 2nd Edition, 2/03
Specifying the amount of data to transfer
The second LD instruction indicates the
amount of data that needs to be transferred (in
bytes, 128 maximum). You have to specify the
amount of data in complete bytes. For
example, Y0 – Y27 would be three bytes of
data. There are 24 bits for the output range of
Y0–Y27 (these I/O addresses are in octal).
From the charts below we see that we can
obtain 8 bits per byte for this type of memory.
Therefore, 24 bits yields 3 bytes, of 8 bits each.
The charts below can be very helpful. Notice
that the different PLC families do not always
use the same types of memory or the same
byte boundaries. For example, the DL305 does
not use a separate data type for input and
output points.
Example:
3 bytes of data to be transferred
Number of Bytes
in decimal
LD
K201
LD
K3
The number of bytes specified also depends on the type of data you want to obtain. For
example, the DL405 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
Direct LOGIC

products.
DL 205 / 405 Memory Bits per unit Bytes
V memory
T / C current value
16
16
2
2
Inputs (X, GX, SP) 8 1
Outputs
(Y, C, Stage, T/C bits) 8 1
Diagnostic Status 8 1
DL305 Memory Bits per unit Number of
bytes
Data registers
T / C accumulator
8
16
1
2
I/O, internal relays, shift
register bits, T/C bits,
stage bits 1 1
Diagnostic Status
(5 word R/W) 16 10