Mailbox - WAGO I/O-SYSTEM 750 Manual

54 Process Image
Whether process data is overlaid by data from register or Mailbox data or process
data is made invalid is controlled by specific bits in the control byte (see section
"Control/Status Byte (C/S Byte)").
6.3.1

Mailbox

The 750-644 I/O module provides a protocol referred to as "Mailbox" below for
parameterization and diagnostics. The protocol allows data exchange between the
750-644 I/O module and a PLC application.
The Mailbox of the 750-644 I/O module is not a permanent part of the process
image, but may be mapped as required. If the Mailbox is mapped, part of the
process image is no longer available for exchanging process data with remote
devices.
If bit 5 is set in the control byte in the output process image (PIO), it is viewed as
a request to the 750-644 I/O module to map the Mailbox. The 750-644 I/O
module responds to the request by setting bit 5 in the status byte. The Mailbox is
thus considered mapped. If the Mailbox is mapped, it can be used to parameterize
the I/O module or to query status or diagnostic information.
The Mailbox begins after the control/status byte and the internal byte with the 3
byte of the process image and, depending on the size set, covers 6, 12 or 18 bytes
of the process image (see section "Process Image" > ... > "Process Data Overlaid
by Mailbox").
The Mailbox size determines which mailbox commands can be executed!
To configure with WAGO-I/O-CHECK or function blocks of the WAGO-I/O-
PRO CAA, you can choose each available Mailbox size independent of fieldbus
limitations.
• For successful configuration, a Mailbox size of at least 12 bytes is
necessary.
• If all diagnostic commands are to be fully available, a Mailbox size of 18
bytes is required.
If you are using a fieldbus over which less than 20 bytes per data element can be
transmitted (e.g. CANopen), you should reduce the Mailbox size again to an
appropriate size after successfully completing the device configuration.
In the area of the process image overlaid by the Mailbox, the data is interpreted as
Mailbox data, so commands (Opcodes) can be sent here. The structure of the data
in the Mailbox is always identical:
WAGO-I/O-SYSTEM 750
750-644 Bluetooth
Version 2.0.0, valid from FW/HW Version 03/03
®
RF-Transceiver
rd
Manual