Input / Output Mailbox - Omron C200HW-PRM21 Operation Manuals

Input / Output Mailbox

5-2

Input / Output Mailbox

PROFIBUS-DP specific
commands
Beside the input and output buffer, the Unit also contains an input mailbox
and an output mailbox. PROFIBUS-DP specific commands can be transferred
from the CPU to the output mailbox. The response to the command placed in
the output mailbox will be placed in the input mailbox. This response can then
be read by to the CPU.
There are two ways to transfer a command to the output mailbox.
1. Issuing a command by IOWR instruction in the PLC program. The
contents of the data area specified by the IOWR instruction are transferred
to the output mailbox.
2. Via the control words. The most common PROFIBUS-DP control
commands can be selected by activating the corresponding bit in the
control word IR n. The Unit will interpret this control word and place the
corresponding command in the output mailbox.
Responses to these common control commands are automatically removed
from the input mailbox. These responses contain no valuable information for
the user.
Responses to other commands - issued via IOWR instructions - should be
read from the input mailbox with the IORD instruction. If this is omitted, the
input mailbox buffer will fill up. When this is the case, the output mailbox will
be disabled; it will not be possible to transfer commands to the output mailbox
anymore. Once the input mailbox is emptied again, the outstanding
commands in the output mailbox will be processed by the unit.
Details about the IOWR and IORD instructions are given in section 6.
Note The input mailbox can also be cleared using control word IR n. The
status of the mailboxes is indicated in the status word IR n+2.
Section 5-2
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