Special Characteristics of the ACS / DCS Drives Communication via MODBUS RTU Library¶
The Function Blocks in the ACSDrivesComModRTU_AC500_V20 Library are designed to handle the MODBUS RTU communication to 1 or more drives.
The Function Blocks ACSxxxx_COM_MOD_RTU perform all the actions that are needed to read and write MODBUS RTU jobs from / to different slaves.
The data handling is automatically done in the ACSxxxx_COM_MOD_RTU Function Blocks using the COM_MOD_MAST and ACS_COM_READ_N_PRM and ACS_COM_WRITE_N_PRM Function Blocks internally.
The user just has to connect the communication Function Blocks together via the common LINE_TOKEN variable of type ACS_MOD_TOKEN_TYPE.
The following block diagram shows the general connection of the Function Blocks for 3 drives:
Function Block Diagram PS553-DRIVES library MODBUS RTU connection for three ACS drives
The communication Function Blocks are connected together via the LineToken variable. All Function Blocks regarding 1 drive are connected together via the DRIVE_DATA variable of type ACS_DRIVE_DATA_TYPE.
For the MODBUS settings in the AC500 see tab PLC configuration \ Interfaces \ COMx – Modbus \ Module parameters – or in ABB Automation Builder: Setting_COMx_Modbus
For the MODBUS settings in the ACS drives see Parameter group “EFB Protocoll”, e.g. Par. 53.02 .. 53.04 for ACS355.
Performance
The following timing performance has been measured:
Test was done with no change of commands nor reference values. So just a continuous reading of status values from each drive were performed.
Test conditions general: PM554-T, timeout at ACS3XX_COM_MOD_RTU: 1000 ms
| Baudrate | Number of drives | Update time for 1 drive | ||
|---|---|---|---|---|
| - | - | PLC scan time: 10ms PLC load: 50% | PLC scan time: 5ms PLC load: 74% | PLC scan time: 3ms PLC load: 75% |
| 19,2 kBd | 7 | 450 ms | 360 ms | - |
| 19,2 kBd | 3 | 190 ms | - | 147 ms |
| 115,2 kBd | 7 | 370 ms | 280 ms | - |
| 115,2 kBd | 3 | 160 ms | - | 100 ms |