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5. Modbus Slave Mode
The I-7530A-MR, Modbus RTU to CAN converter, supports the Modbus
RTU protocol. It can act as a Modbus RTU slave on the Modbus network. There
are some mechanisms for data-exchanging between the CAN register and the
Modbus RTU register as the figure at the next page.
In the Modbus Input Register, according to the different purposes these
register are divided into three fields, "Normal CAN Message Field", "Specific
CAN Message Field" and "Module Status Field". When a CAN message
received from the CAN network, the I-7530A-MR will check if the Specific CAN
Message filed is used or not. If it is not used, this CAN message will be stored
into the "Normal CAN Message" field. This filed is similar with a kind of FIFO
(first-in first-out buffer). Users can only read this field with the start address of
this field by applying the Modbus commands. After users read the CAN
messages from this filed, the rest unread CAN messages will be moved to the
buffer with the start address of this field. This field can store maximum 200 CAN
messages. Therefore, if the unread CAN messages exceed 200 records, the
data is lost.
If the Specific CAN Message filed is used, the CAN messages which are
marked in the specific CAN message table of the Utility tool are directly moved
to the Specific CAN Message field. CAN messages with different CAN IDs will
be stored in different parts of the Specific CAN Message field. Users can set
maximum 10 different CAN ID of CAN messages (firmware v1.02 or later
support 100 CAN ID of CAN messages). Besides, a kind of CAN ID only has
one record buffer. If there are two CAN messages with the same ID, the later
will over-write the former. Therefore, the Specific CAN Message filed always
keeps the newest information of the corresponding CAN messages with the
specific CAN IDs.
If a CAN message is sent to a CAN network from a Modbus network via the
I-7530A-MR, the CAN message will be temporarily stored in Output Register
and not be transmitted until the CAN bus idle. The Output Register is only one
message buffer. If the data overrun is happened, users will get an error code for
replying. Users can also use Modbus RTU command to read the CAN message
transmitted before. It is helpful for checking the last sent record.
I-7530A-MR Modbus RTU to CAN Converter User's Manual (Version 1.07, 06/2016) ------------- 62
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