7 Application Instructions API 50-99 9. The relation between special data registers and interrupts is described below. (Only lower 8 bits are valid.) Three communication interrupts at most can be enabled by the program in a DVP-EH3/SV2 series PLC. Users have to note the interrupt numbers used. (DVP-SV2 series PLCs do not support COM3.) The interrupts I151, I161, I153, and I163 only support EH3/EH3-L/SV2 V2.00 (and above). EH2 and SV only support COM2 communucation interrupts. 10. M1143 is for the selection of ASCII mode or RTU mode. On = RTU mode; Off = ASCII mode. Take the standard Modbus format for example:
In ASCII mode (M1143 = Off) The communication protocol is in Modbus ASCII mode, i.e. every byte is composed of 2 ASCII characters. For example, 64Hex is ‘64’ in ASCII, composed by ‘6’ (36Hex) and ‘4’ (34Hex). Every hex ‘0’…’9’, ‘A’…’F’ corresponds to an ASCII code. DVP-PLC APPLICATION MANUAL 7-113 Communication port Interrupt number Special data register COM1 I151 D1397 I161 D1398 COM2 I150 D1168 D160 D1169 I170 - COM3 I153 D1242 I163 D1243 STX Start word = ‘:’ (3AH) Address Hi Communication address: The 8-bit address consists of 2 ASCII codes Address Lo Function Hi Function code: The 8-bit function code consists of 2 ASCII codes Function Lo DATA (n-1) Data:
The n × 8-bit data consists of 2n ASCll codes ……. DATA 0 LRC CHK Hi LRC checksum: The 8-bit checksum consists of 2 ASCll code LRC CHK Lo END Hi End word: END Hi = CR (0DH), END Lo = LF(0AH) END Lo Character ‘0’ ‘1’ ‘2’ ‘3’ ‘4’ ‘5’ ‘6’ ‘7’ ASCII code 30H 31H 32H 33H 34H 35H 36H 37H Character ‘8’ ‘9’ ‘A’ ‘B’ ‘C’ ‘D’ ‘E’ ‘F’ ASCII code 38H 39H 41H 42H 43H 44H 45H 46H