Siemens SIMATIC S7-1200 - Page 989

Communication
11.5 S7 communication
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
989
You must ensure that the length (number of bytes) and data types for the ADDR_x (remote
CPU) and RD_x or SD_x (local CPU) parameters match. The number after the identifier
"Byte" is the number of bytes referenced by the ADDR_x, RD_x, or SD_x parameter.
Note
The total number of bytes received on a GET instruction or the total number of bytes sent on
a PUT instruction is limited.
The limitations are based on how many of the four possible
address and memory areas you use:
•
If you use only ADDR_1 and RD_1/SD_1, a GET instruction can get 222 bytes and a PUT
instruction can send 212 bytes.
•
If you use ADDR_1, RD_1/SD_1, ADDR_2, and RD_2/SD_2, a GET instruction can get a
total of 218 bytes and a PUT instruction can send a total of 196 bytes.
•
If you use ADDR_1, RD_1/SD_1, ADDR_2, RD_2/SD_2, ADDR_3, and RD_3/SD_3 a
GET instruction can get a total of 214 bytes and a PUT instruction can send
a total of 180
bytes.
•
If you use ADDR_1, RD_1/SD_1, ADDR_2, RD_2/SD_2, ADDR_3, RD_3/SD_3, ADDR_4,
RD_4/SD_4 a GET instruction can get a total of 210 bytes and a PUT instruction can
send a total of 164 bytes.
The sum of the number of bytes of each of your a
ddress and memory area parameters must
be less than or equal to the defined limits. If you exceed these limits, the GET or PUT
instruction returns an error.
On the rising edge of the REQ parameter, the read operation (GET) or write operation (PUT)
loads the ID, ADDR_1, and RD_1 (GET) or SD_1 (PUT) parameters.
● For GET: The remote CPU returns the requested data to the receive areas (RD_x),
starting with the next scan. When the read operation has completed without error, the
NDR parameter is set to 1. A new operation can only be started after the previous
operation has completed.
● For PUT: The local CPU starts sending the data (SD_x) to the memory location (ADDR_x)
in the remote CPU. When the write operation has completed without error, the remote
CPU returns an execution acknowledgement. The DONE parameter of the PUT
instruction is then set to 1. A new write operation can only be started after the previous
operation has completed.
Note
To ensure data consistency, always evaluate when the operation has be
en completed
(NDR
= 1 for GET, or DONE = 1 for PUT) before accessing the data or initiating another
read or write operation.