12: M ODBUS ASCII/RTU C OMMUNICATIONFC5A MICROS MART U SER’ S MANUAL FC9Y-B1268 12-11Modbus Slave CommunicationModbus slave communication is made possible by selecting Modbus ASCII Slave or Modbus RTU Slave for port 1 to port 7in the WindLDR Function Area Settings. When a Modbus slave receives a request from the Modbus master, the Modbusslave reads or writes data according to the request. The request is processed at the END processing of the user program.Modbus Slave Communication SpecificationsMode ASCII Mode RTU ModeBaud Rate (bps) *1 9600, 19200, 38400, 57600, 115200Data Bits 7 bits (fixed) 8 bits (fixed)Stop bits 1, 2 bitsParity Odd, even, noneSlave Number 1 to 311 to 247 (CPU modules with system program version 110 or higher)Response Time *2 1 to 5000 ms(in increments of 1 ms)Timeout between Characters *3 —*4 1.5 characters minimum *5Timeout between Frames *3 —*4 3.5 characters minimum *6*1: 115200 bps can be selected when FC5A-SIF4 is used on port 3 through port 7.*2: D8054 is a special data register for Modbus communication transmission wait time (1 ms) for port 2. 0 designates 1 ms, and 5000or more designates 5000 ms. Using D8054 can delay transmission from the MicroSmart. When port 1 or 3 through 7 are used, theresponse time is 1 ms.*3: When timeout occurs, the MicroSmart discards the received data and waits for the first frame of the next valid communication.*4: ASCII mode finds the beginning of a frame by the “:” code. While the MicroSmart is receiving an incoming request message and atthe same time receives a “:” code, the MicroSmart discards the received data and waits for a slave number.*5: For communication at 19200 bps or higher, space between characters needs to be a minimum of 0.75 ms.*6: For communication at 19200 bps or higher, space between frames needs to be a minimum of 1.75 ms.Communication Completion and Communication ErrorModbus communication finishes when a read or write process is completed successfully or when a communication erroroccurs. Immediately after a request communication has been completed, Modbus communication completion relayM8080 turns on for 1 scan time. When a communication error occurs, the error code is stored to special data registerD8053. The data in D8053 is valid only for the 1 scan time when M8080 is on.When a communication error occurs, communication error special internal relay M8005 also turns on for 1 scan timeimmediately after the error.M8080 and D8053 are used only when Modbus master is used on port 2.Phone: 800.894.0412 - Fax: 888.723.4773 - Web: www.clrwtr.com - Email: info@clrwtr.com
