WAGO -I/O-SYSTEM 750 Series Manual page 24

24 • 750-655 [AS-Interface master module]
Process image
Mode 3 is reserved for register communication. Bit 2
to activate register communication. Resetting this bit switches register
communication off again. The selected setting is mirrored in bit 2
status byte. The register data are superimposed on the PI offset byte 2 and byte
3 over the respective cyclical or acyclical memory range depending on the
selected mode.
Note
In Mode 3, the mailbox and the process data are basically no longer valid.
Process image length and mailbox length:
The process image length and the mailbox length can be freely set within fixed
limits with the limitation that the process image length is greater than the
mailbox length plus two control/status bytes.
The size of the process image can be set to 12 bytes, 20 bytes, 24 bytes, 32
bytes, 40 bytes or 48 bytes.
The mailbox length can be set to 0 bytes, 6 bytes, 10 bytes, 12 bytes or 18
bytes.
Note
If a mailbox length of 0 bytes is set, it will only be possible to access the
process data of digital slaves.
AS-Interface process data:
The length of the AS-Interface data and thus the number of transferable slaves
is given by the combination of the above-mentioned process image and
mailbox settings.
AS-Interface process data length = (Process image length – Mailbox length – 2)
The following table shows a summary of the permissible configurations of
process image and mailbox:
7
in the control byte is set
7
of the
WAGO-I/O-SYSTEM 750
I/O Modules