add Modbus03Rx.getRegBegin

core/components/modbus/modbus.hpp

@@ -41,6 +41,7 @@ class Modbus03Rx {
     uint16_t* reg = (uint16_t*)MODBUS_GET_REG_START(rx.data());
     return MODBUS_GET_REG(reg[index]);
   }
+  uint8_t* getRegBegin() { return (uint8_t*)MODBUS_GET_REG_START(rx.data()); }
 };
 
 class ModbusMaster {
@@ -98,7 +99,6 @@ class ModbusMaster {
    * @return int
    */
   int modbus10(uint8_t deviceid, uint16_t startreg, uint16_t regnum, uint16_t* txreg, uint32_t overtime);
-
 };
 }  // namespace core
 }  // namespace iflytop