AS-Interface
Profibus-DP
Subject to reasonable modifications due to technical advances.
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For the programming of AS-i Control, the I/O field is further enlarged by 5-17 addition-
al bytes. They contain an identification byte (read/write/start/stop), the base address
and 2-14 bytes user data. It is not possible to read and write at the same time.
Transmission of user memory
User memory can be transmitted in the I/O field by adding bytes for the memory loca-
tions to be written (O-field) or to be read (I-field). The amount of user memory to be
written or read can be different.
8.2.1
Mapping of the AS-i Data in the Profibus-DP Telegram
The data in the DP telegram is always mapped in the same fixed order:
• AS-i I/O data
• AS-i parameters
• AS-i Control code
• user memory
If some elements are missing (e.g. no transfer of the AS-i Control code), subsequent
elements are added directly.
The individual parts of the DP-telegram are coded as follows:
with
K =
number of AS-i 1
(instead of slave 0 the AS-i flags are transmitted)
N =
K/2
M = number of user memory bytes up to 128 bytes
L =
number of bytes of AS-i Control code
(calculated out of value in element selection of the user-parameter telegram)
N bytes
AS-i I/O data
2 bytes
AS-i parameter
5-17 bytes
AS-i Control
code
M bytes
user memory
user memory 0..
user memory M-1
high address, control byte
low-address, L bytes data
AS-i slave address, AS-i parameter
byte 0.
..
byte N-1
slave 1 AS-i flags
...
slave (K-1) slave (K-2)
