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µC/Modbus is initialized by simply calling MB_Init() and specifying the Modbus RTU frequency as an argument. Once initialized, you simply need to configure each Modbus channels (using MB_CfgCh()) as shown in the example below. Here, our product has three Modbus ports: a Modbus RTU port communicating at 9600 baud and a Modbus ASCII port communicating at 19200 baud and a Modbus ASCII Master port communicating at 19200 baud. Both Modbus Slave ports assume Modbus address 1 but, you can specify different node address for each one if you want.

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MB_Init(1000);              // Initialize uC/Modbus, RTU timer at 1000 Hz

MB_CfgCh(   1,              // ... Modbus Node # for this slave channel
         MODBUS_SLAVE,      // ... This is a SLAVE
            0,              // ... 0 when a slave
         MODBUS_MODE_RTU,   // ... Modbus Mode (_ASCII or _RTU)
            1,              // ... Specify UART #1
         9600,              // ... Baud Rate   
            8,              // ... Number of data bits 7 or 8 
         MODBUS_PARITY_NONE,// ... Parity: _NONE, _ODD or _EVEN   1,
                            // ... Number of stop bits 1 or 2
         MODBUS_WR_EN);     // ... Enable (_EN) or disable (_DIS) writes

MB_CfgCh(   1,              // ... Modbus Node # for this slave channel
         MODBUS_SLAVE,      // ... This is a SLAVE
            0,              // ... 0 when a slave
         MODBUS_MODE_ASCII, // ... Modbus Mode (_ASCII or _RTU)
            1,              // ... Specify UART #2
        19200,              // ... Baud Rate
            8,              // ... Number of data bits 7 or 8
         MODBUS_PARITY_NONE,// ... Parity: _NONE, _ODD or _EVEN
            1,              // ... Number of stop bits 1 or 2
         MODBUS_WR_EN);     // ... Enable (_EN) or disable (_DIS) writes

Important

If your application is using a RTOS interface, once a µC/Modbus-S channel has been configured, you do not need to do anything else in your code. In other words, a Modbus master can start communicating with your Modbus slave without having to add any additional code in your application tasks! Refer to section 7 for details on how this works.

If your application is not using a RTOS interface, once a µC/Modbus-S channel has been configured, your application needs to call MB_OS_RxTask()to poll the Modbus Slave channels. Refer to section 8 for details on how this works.

MB_CfgCh(   1,              // ... Modbus Node # for this slave channel
         MODBUS_MASTER,     // ... This is a MASTER
         OS_TICKS_PER_SEC,  // ... One second timeout waiting for slave response
         MODBUS_MODE_ASCII, // ... Modbus Mode (_ASCII or _RTU)
            2,              // ... Specify UART #3 
        19200,              // ... Baud Rate
            8,              // ... Number of data bits 7 or 8
         MODBUS_PARITY_NONE,// ... Parity: _NONE, _ODD or _EVEN
            1,              // ... Number of stop bits 1 or 2
         MODBUS_WR_EN);     // ... Enable (_EN) or disable (_DIS) writes

Important

Once a µC/Modbus-M channel has been configured, your application code needs to call MBM_FC??_???() functions as described in this section in order to obtain data from Modbus slaves connected to that channel. Refer to section 8 for details on how this works.

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