8. Modbus Station Address Selection
The MDB-100 interface provides two different methods for configuring the node’s station address. One method uses the inverter number parameter read from the drive connected to Channel A, and the other method uses a locally-configured address, set by DIP switches on the MDB-100 control PCB.
When shipped from the factory, the MDB-100’s default configuration is to use the value set in the inverter number parameter (F802) of the drive connected to Channel A as its Modbus network station address. Depending on the software version of the drive connected to channel A, this parameter is adjustable from either 0∼ 31 or 0∼ 63.
Since Modbus addressing allows for station addresses to be set from 1 ∼ 247, however, there may be instances where the upper limit of the inverter number parameter setting is not high enough to support a desired address (for example, if you want to set a MDB-100 station to address 95) In these instances, the locally- configured station address can be used, which supports the full Modbus station addressing range of 1 ∼ 247.
Note that the Modbus protocol specification states that allowable station addresses are 1 to 247. If a station address is configured with 0 (inverter number or local address) or 248 to 255 (local address only), the MDB-100 will halt and will not communicate with the network. To resolve this situation, correct the station number and reset the MDB-100. Pay particular attention to this point, as the default factory setting of the drive’s “inverter number” parameter is 0, which therefore must be changed if it is to be used as the MDB-100’s station number.
The selection of whether to use the drive on Channel A’s inverter number parameter or the locally-set station address is performed by switch SW1 #8. When SW1 #8 is OFF (factory default setting), the MDB-100’s station address is retrieved from drive A’s inverter number parameter. When SW1 #8 is ON, the MDB-100’s station address is obtained by the binary number set via DIP switch SW2 (factory default address setting = 1).
SW1 #8 | Meaning |
OFF | Drive A’s inverter number parameter (factory default) |
ON | Switch SW2 address setting |
The values of switches SW1 and SW2 are read only during MDB-100 initialization. Therefore, if any of these switch settings are changed, the MDB-100 must be reinitialized to be made aware of the change by:
1.Momentarily powering-off drive A (from which the MDB-100 receives power), or
2.Issuing a reset command to the MDB-100 via the Modbus network by writing to holding register 0x6111NOTE 1, NOTE 2. Writing data 0x5A5A will reset the MDB-100, writing data 0xFEBA will reset the MDB-100 and return all MDB-100 –specific configuration registers (such as response delay time, loss of communications timeout time etc.) to their factory default values, and writing any other data will cause the MDB-100 to return a Modbus “ILLEGAL DATA VALUE” exception response (exception code 03). Reading from register 0x6111 will always return a value of 0.
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