diff --git a/MCU_STM32F4xx_Matlab/STM32F4xx_SIMULINK/stm32f4xx_matlab_tim.c b/MCU_STM32F4xx_Matlab/STM32F4xx_SIMULINK/stm32f4xx_matlab_tim.c
index c3c83ee..f8abd82 100644
--- a/MCU_STM32F4xx_Matlab/STM32F4xx_SIMULINK/stm32f4xx_matlab_tim.c
+++ b/MCU_STM32F4xx_Matlab/STM32F4xx_SIMULINK/stm32f4xx_matlab_tim.c
@@ -65,7 +65,15 @@ void TIMx_Count(TIM_TypeDef* TIMx, struct TIM_Sim* TIMS)
         TIMS->tx_cnt -= TIMS->tx_step / TIMx->PSC;
     else if (((TIMx->CR1 & TIM_CR1_DIR) == 0) && TIMx->CR1) // down COUNTER and COUNTER ENABLE
         TIMS->tx_cnt += TIMS->tx_step / TIMx->PSC;
-    TIMx->CNT = (uint32_t)TIMS->tx_cnt;
+
+    if (TIMS->tx_cnt > 0)
+    {
+        TIMx->CNT = (uint32_t)TIMS->tx_cnt;
+    }
+    else
+    {
+        TIMx->CNT = 0;
+    }
 }
 
 /**
@@ -85,13 +93,17 @@ void Overflow_Check(TIM_TypeDef* TIMx, struct TIM_Sim* TIMS)
 
         if (TIMS->tx_cnt > TIMS->RELOAD || TIMS->tx_cnt < 0) // OVERFLOW
         {
+            TIMS->RELOAD = TIMx->ARR; // RELOAD ARR
 
             switch (TIMx->CR1 & TIM_CR1_CMS)
             {
             case TIM_COUNTERMODE_CENTERALIGNED1:
             case TIM_COUNTERMODE_CENTERALIGNED2:
             case TIM_COUNTERMODE_CENTERALIGNED3:
-                TIMx->CR1 ^= TIM_CR1_DIR;
+                if(TIMS->tx_cnt > TIMS->RELOAD)
+                    TIMx->CR1 |= TIM_CR1_DIR;
+                else if(TIMS->tx_cnt < 0)
+                    TIMx->CR1 &= ~TIM_CR1_DIR;
 
                 if (TIMx->DIER & TIM_DIER_UIE) // if update interrupt enable
                     call_IRQHandller(TIMx); // call HANDLER
@@ -99,7 +111,6 @@ void Overflow_Check(TIM_TypeDef* TIMx, struct TIM_Sim* TIMS)
 
             // default counting
             default:
-                TIMS->RELOAD = TIMx->ARR; // RELOAD ARR
 
                 if (TIMS->tx_cnt > TIMx->ARR) // reset COUNTER
                     TIMS->tx_cnt = 0;
diff --git a/mcu_test_r2021a.slx b/mcu_test_r2021a.slx
index 8f4752b..04cf205 100644
Binary files a/mcu_test_r2021a.slx and b/mcu_test_r2021a.slx differ