2. FX series PLC communication agreement of mitsubishi PLC FX system communication

PC communication protocols must be based on the connected PLC to write communication protocols, so we have to be familiar with the FX series PLC communication protocol. 1) Using asynchronous format, data format of FX series PLC by one start bit, seven data bits, one parity bit and 1 stop bit, bit rate is 9600 BPS, character for ASC Ⅱ yards. The data format is shown in figure 7 14. Figure 7 - 14 data format (2) Communication command FX series PLC has four communication command, were read command, write command, force command, forced off, such as table 7 - 2. Table 7 - 2 FX series PLC communication command table 3) FX series PLC communication control characters using character-oriented communication procedures, using five communication control characters, such as table 7 - 3. Table 7 - 3 FX series PLC controller communication control character table control character code ASC Ⅱ detail request ENQ05HPC ACK06HPLC confirmed answer of ENQ NAK15HPLC ENQ denied answer STX02H information frame start marks ETX03H information frame end note: when the ENQ from the PLC to the computer don't understand, answered with a NAK. 4) Message format to the PLC computer sends a packet format is as follows: STXCMD ETXSUMHSUML data among them, STX to start sign: 02 h; ETX as end mark: 3 h; CMD ASC Ⅱ code for the command; SUMH, SUML in bytes and accumulation and overflow. Because the two bytes of each byte hexadecimal number into ASC Ⅱ code, it is with SUML SUMH checksum. Data format and meaning is as follows: note: write command data segment data, read data segments are countless according to command. PLC to PC, and the response message format is as follows: note: to read command response message data segment to read data, a data of two bytes, in upper lower: data segments: a reply message to write command numerous according to section, and with an ACK and NAK reply content. 5) Transmission procedures using response communication between PC and FX series PLC controller, transmission error and the organization. As shown in figure 7 - its transport process 15. Figure 7 - 15 the transmission process of PLC controller according to the command of PC, at the END of each loop scanning the END statement after automatic reply, without user in PLC programming.
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