Schneider Electric LUFP9 - page 34

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5. Gateway Initialization and Diagnostics
Bits Description
14 FB_HS_SEND: New command from the DeviceNet master
Before changing the value of FB_DU, the DeviceNet master must compare the values of
FB_HS_SEND and ABC_HS_CONFIRM (bit 14 of the gateway’s status word). If these two values are
different, this means that the gateway has not yet acknowledged the previous DeviceNet master
command. Else, the DeviceNet master can issue a new command, updating the FB_DU bit according
to the nature of its command (shutdown or activation of Modbus exchanges), then toggling the value
of the FB_HS_SEND bit to inform the gateway that it has sent it a new command.
Summary:
• If ( FB_HS_SEND ≠ ABC_HS_CONFIRM ) Æ The DeviceNet master command word still
contains a command which has not yet been acknowledged by the gateway. So the DeviceNet
master cannot use this word to place a new command in it.
• Else Æ The previous command of the DeviceNet master has been acknowledged by the
gateway, which allows it to transmit a new command. In this case, it changes the value of the
FB_DU bit, then toggles the value of the FB_HS_SEND bit.
13 FB_DU: Modbus exchange startup
The setting of this bit to one by the DeviceNet master allows communications between the gateway
and the Modbus slaves. Resetting it to zero is used to inhibit them.
When the DeviceNet master sets this bit to one, it is preferable for all of the output data it has placed
in the gateway’s output memory to be up-to-date (“FB_DU” means “FieldBus – Data Updated”). If
they are not, this data will be transmitted to the Modbus slaves “as it”.
0-12 Reserved.
Due to the inversion of the LSB and the MSB for this register between the gateway and the DeviceNet master,
the structure of the corresponding output word (“O:1.1” in the case of the default configuration) is as follows:
Bits Description
8-15 Reserved.
7FB_HS_CONFIRM: Acknowledgement bit of a gateway diagnostic
6FB_HS_SEND: New DeviceNet master command word
5FB_DU: Modbus exchange startup
0-4 Reserved.
e.g. If the O:1.1 output word is set to 16#00A0, the DeviceNet master command word will be set to 16#A000.
The correct use of this command word by the DeviceNet master, to transmit a new command to the gateway,
goes through the following steps:
• Checking of (FB_HS_SEND = ABC_HS_CONFIRM).
• The command, that is to say the value of the FB_DU bit, is updated.
• The value of the FB_HS_SEND bit is inverted.
N.B. It is possible to simplify this use as follows:
• The FB_DU and FB_HS_SEND bits are set to one to activate the Modbus communications.
• The FB_DU and FB_HS_SEND bits are reset to halt Modbus communications.
On the other hand, do not write directly in 16-bit format in the DeviceNet master command word, because this
would disrupt the operation of the transfer of the gateway diagnostics (undesired change to FB_HS_CONFIRM).
However, during some debug or test phase, you could, for instance, write 16#6000 in the DeviceNet master
command word (that is to say 16#0060 in the O:1.1 output word) in order to activate the Modbus
communications, and 16#0000 to stop them.