5. Gateway Initialization and Diagnostics
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 input word (“I:1.1” in the case of the default configuration) is as follows:
Bits | Description |
ED: Error data item associated with the Modbus network | |
7 | ABC_HS_SEND: New gateway diagnostic |
6 | Reserved. |
5 | ABC_DU: Modbus exchanges activated |
4 | Periodicity of Modbus exchanges |
EC: Error code associated with the Modbus network |
E.g. If the gateway’s status word is set to 16#B031, the input word I:1.1 will be set to 16#31B0.
The correct use of this status word by the DeviceNet master, to read a diagnostic generated by the gateway, goes through the following steps:
•Checking of (ABC_HS_SEND ≠ FB_HS_CONFIRM).
• Reading of the value of ABC_DU to determine whether all of the Modbus inputdata are
• Reading of the value of the “Periodicity of Modbus exchanges” bit to determine whether the periodicity of the Modbus communications has been maintained.
• Reading of the values of EC and ED to check for any error detected by the gateway on the Modbus network (see table on page 36).
• Copying of the value of the ABC_HS_SEND bit to the FB_HS_CONFIRM bit.
This last step is essential because it allows the gateway to transmit a future diagnostic! Even if you do not wish to read the content of the gateway’s status word, it is preferable to automate this step in your DeviceNet master software.
5.2.2. DeviceNet Master Command Word
The output word located at addresses 16#0200 (MSB) and 16#0201 (LSB) in the gateway’s output memory constitutes the DeviceNet master command word. Its structure is described below:
Bits | Description |
15 | FB_HS_CONFIRM: Acknowledgement bit of a gateway diagnostic |
| The DeviceNet master must compare the value of the FB_HS_CONFIRM bit to the value of the |
| ABC_HS_SEND bit (bit 15 in the gateway’s status word). If these two values are different, this means |
| that the gateway has transmitted a new diagnostic to the DeviceNet master. |
| To tell the gateway that it has read a diagnostic, the DeviceNet master must copy the value of the |
| ABC_HS_SEND bit to the FB_HS_CONFIRM bit. This allows the gateway to issue a new diagnostic. |
| Summary: |
•If ( FB_HS_CONFIRM = ABC_HS_SEND ) Æ The gateway’s status word contains a diagnostic which has already been acknowledged by the DeviceNet master. So the gateway is free to use this status word to place another diagnostic there.
•Else Æ A new diagnostic is available in the gateway’s status word. The DeviceNet master can read this diagnostic, but must also copy the value of ABC_HS_SEND to FB_HS_CONFIRM in order to allow the gateway to generate new diagnostics.
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