feat: Modbus 新增 0x0012 系统指令寄存器，写 0x2C2C 复位 MCU (对齐 700BS 0x2C)

BLE/DLD154Pro_Peripheral_28K/APP/rs485_modbus.c

@@ -550,6 +550,8 @@ static uint8_t read_hr_register(uint16_t addr, uint8_t *hi, uint8_t *lo)
         *hi = 0; *lo = _auto_rpt_enable; return 1;
     case 0x0011: /* Active Threshold */
         *hi = (uint8_t)(_active_threshold >> 8); *lo = (uint8_t)(_active_threshold); return 1;
+    case 0x0012: /* System Cmd (只读, 恒为 0) */
+        *hi = 0; *lo = 0; return 1;
     default:
         return 0;
     }
@@ -653,6 +655,12 @@ static void handle_write_single_reg(const uint8_t *rx, uint8_t rx_len)
     case 0x0011: /* Active Threshold: 0-65535 */
         _active_threshold = reg_val;
         break;
+    case 0x0012: /* System Cmd: 写 0x2C2C 复位 MCU */
+        if (reg_val == MB_CMD_RESET_MCU) {
+            SYS_ResetExecute();
+        }
+        /* 非法值: 忽略, 不响应异常 (对齐 700BS 0x2C 行为) */
+        return;
     default:
         send_exception(0x06, 0x02);  /* Illegal Data Address */
         return;
@@ -723,6 +731,13 @@ static void handle_write_multiple_regs(const uint8_t *rx, uint8_t rx_len)
                      if (_auto_rpt_enable) { _rpt_last_ms = mstick(); _rpt_active = 0; _rpt_hyst_cnt = 0; }
                      break;
         case 0x0011: _active_threshold = reg_val; break;
+        case 0x0012: /* System Cmd: 写 0x2C2C 复位 MCU */
+                     if (reg_val == MB_CMD_RESET_MCU) {
+                         SYS_ResetExecute();
+                         return;  /* 不复位则忽略非法值 */
+                     }
+                     /* 非法值: 忽略, 继续后续寄存器 */
+                     break;
         default:     send_exception(0x10, 0x02); return;
         }
     }