LPC812: What is the Clock input for UART0 ?

[karthikvenkates]

Hi,

Above is the UART Clock generation diagram given in LPC812 datasheet.

My question is:

#1. Based on the explanation given in datasheet, I understand that Any peripherals in LPC812 require System clock to operate. So obviously UART0 also need that as input as shown above.

      At the same time, for the UART0 baud rate generation, we are using a derivative of main clock. So what exactly is the purpose of System Clock in UART0 ?

#2. Is it like, for all operation except for the shifting of TX/RX buffer and holding register, UART0 block uses System Clock? 

#3. Even in SYSCON block diagram datasheet says System clock sources Peripherals at the same time, for baud rate generation, we use main clock. What is the reason ? Why didnt NXP use System clock's derivative itself for baud rate generation block ?

[kerryzhou]

Hi karthik venkatesh,

    Thank you for your interest in NXP LPC product, I would like to provide service for you.

   1. what exactly is the purpose of System Clock in UART0 ?

    Just as the Fig 29. USART clocking which you post.

    System clock is used for the USART module clock, it is used for the register operation.

   2. Yes, just the same as item1.

   3. Even in SYSCON block diagram datasheet says System clock sources Peripherals at the same time, for baud rate generation, we use main clock. What is the reason ? Why didnt NXP use System clock's derivative itself for baud rate generation block ?

      This is the chip design question, to the customer, they just need to know how to use it. Actually, in NXP, there really have some other MCU use the system clock as the baud and module clock at the same time.  In LPC812, you just need to know the baud rate is from the main clock, just take care of the application is OK.

Have a great day,
Kerry

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