USART_CR1 and USART_CR2 Registers in Microcontrollers

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Questions and Answers

Which register should be accessed to send data in the STM Arm microcontroller USART?

BAUD

USART_TDR (correct)

USART_RDR

Control 1

Where is the received data stored in the STM Arm microcontroller USART?

Control 1

USART_TDR

Control 2

USART_RDR (correct)

In the STM Arm microcontroller USART, which action requires writing to a separate register?

Enabling USART

Reading received data

Configuring BAUD rate

Sending data (correct)

Which of the following is NOT a configuration register in the STM Arm microcontroller USART?

USART_RDR Signup and view all the answers

What is the purpose of USART_TDR in the STM Arm microcontroller USART?

To send data Signup and view all the answers

Which register in the STM Arm microcontroller USART directly interacts with the serial transmit pin (TXD)?

USART_TDR Signup and view all the answers

What is the purpose of the RXNE bit in USART?

Stands for Receiver Not Empty, indicating data reception Signup and view all the answers

Which register is responsible for setting the baud rate in USART configuration?

USART2_BRR Signup and view all the answers

In USART configuration, what does the USART_SR register check for?

Data reception status Signup and view all the answers

What is the purpose of the USART2_CR1 register in configuration?

Enabling data reception Signup and view all the answers

Why is it important to enable USART2 after completing the configuration steps?

To start the data reception process Signup and view all the answers

What action does the USART2_read() function in the code perform?

Reads a byte from USART2_DR register for processing Signup and view all the answers

Which control register is responsible for specifying the oversampling rate in USART configuration?

USART2_CR1 Signup and view all the answers

In the context of STM Arm USART, what does the AF7 stand for?

<code>Any Function</code> 7, a multipurpose pin designation Signup and view all the answers

What role does the TXE flag play in USART data transmission?

<code>Transmit Enable</code> flag indicating readiness to send data Signup and view all the answers

Which register enables the USART2 after configuration steps in the provided code snippet?

USART2->CR1 Signup and view all the answers

Study Notes

USART Registers

USART Control 1 (USART_CR1) register: a 32-bit register used to set the number of bits per character (data length) in a frame, among other things.
USART Control 2 (USART_CR2) register: a 32-bit register used for configuration.

USART_CR1 Register Bits

Bit 15: OVER8: Oversampling mode (0: oversampling by 16, 1: oversampling by 8)
Bit 13: UE: USART enable (0: USART prescaler and outputs disabled, 1: USART enabled)
Bit 12: M: Word length (0: 1 Start bit, 8 Data bits, n Stop bit, 1: 1 Start bit, 9 Data bits, n Stop bit)
Bit 7: TXEIE: TXE interrupt enable (0: interrupt is inhibited, 1: an USART interrupt is generated whenever TXE=1)
Bit 6: TCIE: Transmission complete interrupt enable (0: interrupt is inhibited, 1: an USART interrupt is generated whenever TC=1)
Bit 5: RXNEIE: RXNE interrupt enable (0: interrupt is inhibited, 1: an USART interrupt is generated whenever ORE=1 or RXNE=1)
Bit 4: IDLEIE: IDLE interrupt enable (0: interrupt is inhibited, 1: an USART interrupt is generated whenever IDLE=1)
Bit 3: TE: Transmitter enable (0: transmitter is disabled, 1: transmitter is enabled)
Bit 2: RE: Receiver enable (0: receiver is disabled, 1: receiver is enabled and begins searching for a start bit)
Bits 13:12: STOP: STOP bits (00: 1 Stop bit, 01: 0.5 Stop bit, 10: 2 Stop bits, 11: 1.5 Stop bit)
Bit 11: CLKEN: Clock enable (0: SCLK pin disabled, 1: SCLK pin enabled)

USART Data Register (USART_DR)

Used to transmit a byte of data
A write to this register initiates a transmission from the USART
The same register is used for both transmit and receive data in STM Arm microcontrollers

Simplified Block Diagram of USART

Transmit Data register (USART_TDR): used to send data
Receive Data register (USART_RDR): used to store received data
USART peripheral sends out the content of the data transmit register through the serial transmit pin (TXD)
Received data is stored in the Receive Data register (USART_RDR)

Enabling the USART

Before enabling the USART, the bus clock to the USART should be enabled
The USART module should be configured properly before it is enabled
The USART module can be disabled by writing a 0 to the UE bit (UE, USART Enable) of the CR1 register

GPIO Pins Used for USART TxD and RxD

In addition to the USART registers setup, the I/O pins for USART (TxD and RxD) must be configured to use their alternate functions
This is done using the AFRx (Alternative Function Register) registers

Steps to Configure USART for Receiving Data

Enable the Clock to GPIOA
Enable the Clock to USART2
Select the peripheral function AF7 for PA3 (USART2_RxD) pin using the GPIO_MODER and GPIO_AFRL registers
Set the baud rate for USART2 using USART2_BRR register
Configure the CR1 (Control 1) register for oversampling rate, character size (8bit or 9-bit) and enabling receive (RE)
Configure the CR2 (Control 2) register for number of stop bit(s) and so on
Configure the CR3 (Control 3) register for no hardware flow control and so on
Enable USART2 after configuration complete
Wait until the RXNE (Receive Not Empty) bit of the USART_SR register is set
Read a byte from USART2_DR register that was received

Importance of the RXNE Flag Bit

The RXNE flag bit is used to indicate when a character is received
The receiver's shift register receives the start bit indicating that the next bit is the first bit of the character it is about to receive
The character is received one bit at a time

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Description

Learn about the USART Control 1 (USART_CR1) register and USART Control 2 (USART_CR2) register in microcontrollers. Understand how these 32-bit registers are used to control aspects like data length and oversampling modes in USART communication.