Design and implementation of extending PLC output points based on SPI bus
Teng Zhu · Microcomputer Information · 2012
In order to provide more available output points for PLC master module and integrate the SPI bus with the shift registers,a new method for extending PLC output points is proposed,and the output expansion circuit is designed.Based on the time serie characteristics of the SPI bus and the shift registers of HC595,select the clock mode of SPI,then matching problem of their series and logical output order are solved.A resistance is connected to UDTY port for insuring it high level,SPI2CLK negated then put into HC595,making sure it get steady data of SPI,improving the circuit anti-interference performances by filter capacitors,the extended output points is controlled by the programming.Practical application indicates that the design method is economic and reliable.