1. Programming Microcontroller
UART - Serial communic.
4- 1
Programming Microcontroller
UART – Universal Asynchronous Receiver Transmitter
Week 4 – Spring Term 2017
32K Byte Burst Flash
64K or 96K Byte SRAM
256K or 512K Byte Burst Flash
OTP Mem
UART
I2C
SPI
TIM
RTC
EXT. Bus
GPIO
USB 2.0FS
CAN 2.0B
Enet MAC
PFQ BC
DMA
INTR Cntl
ARM966E
CORE
w/DSP
96 MHz
CLK Cntl
ADC
LVD BOD
PLL
JTAG
ETM9
STM32F407

2. Typical serial communication (low level)
UART - Serial communic.
4- 2
Full-duplex interface
Device 1
(Data Set)
Receive
Transmit
Device 2
(Data Termial)
Transmit
Receive
-PC
-embedded system
-modem
-barcode reader
-printer
-display (with terminal emulation software)
-data logger
-sensor (simple or complex)
-dongle (security element)
-I/O module (digital, analog, encoder, PT100)
-wireless interface PC
Embedded system

3. RS-232-C pin assignments D-Sub male on PC
UART - Serial communic.
4- 3
Pin
DB9
DB25
Symbol
Direction
Text
Out In 1 8
DCD 
Data Carrier Detect 2 3 Rx
Receive Data Tx 
Transmit Data 4 20
DTR
Data Terminal Ready 5 7
Gnd
Signal Ground 6
DSR
Data Set Ready
RTS
Request to Send
CTS
Clear to Send 9 22 RI
Ring Indicator
Male -> Stecker
Female -> Buchse
RS-232-C: Radio Sector, American Standard since 1969s
EIA: Electronic Industry Alliance

4. Serial data format (logical representation)
UART - Serial communic.
4- 4
1-2 stop bits 1
lsb
msb
5-8 data bits n
Parity bit if enabled
start
time
lsb: least significant bit (20)
msb: most significant bit (2 db-1)
Normally one Byte is sent as 8 data bits
Or: One Byte is sent as 7 data bits + parity
1 bit time = 1 / baudrate
Example: parity enabled, 2 stop bits

5. Start -> Development -> HTerm
UART - Serial communic.
Hyperterminal usage
4- 5
Start -> Development -> HTerm

6. UART – What is it good for?
UART - Serial communic.
UART – What is it good for?
4- 6
Simple serial communication (3-wire)
Multiple physical interfaces:
EIA-232 Peer-to-peer (former RS-232-C 1969). Gnd based ( ,3..15 V)
EIA-485 Party Line, multi-point link (SCSI, ISDN, ...
EIA-422 : Balanced lines, no ground link (D+/D-) on drivers up to 100 kbps. Point-to-point or multi-drop. 0-5 V. Twisted-pair cable
Easy setup
Direct programming
Byte level only
USB will not replace cheap and simple communications
EIA: Electronic Industry Alliance

7. EIA-485 Party Line, multi-point link
UART - Serial communic.
4- 7

8. UART - Serial communic.
Hardware flow control
4- 8
RTS will be switched on and off by programmable receiver FIFO watermarks

9. UART features (1/3) Full duplex, asynchronous communications
UART - Serial communic.
UART features (1/3)
4- 9
Full duplex, asynchronous communications
NRZ standard format (Mark/Space)
Configurable oversampling method by 16 or by 8 to give flexibility between speed and clock tolerance
Fractional baud rate generator systems
Common programmable transmit and receive baud rate (refer to the datasheets for the value of the baud rate at the maximum APB frequency
Programmable data word length (8 or 9 bits)
Configurable stop bits - support for 1 or 2 stop bits
Transmitter clock output for synchronous transmission
IrDA SIR encoder decoder
Support for 3/16 bit duration for normal mode

10. USART features (2/3) Smartcard emulation capability
UART - Serial communic.
USART features (2/3)
4- 10
Smartcard emulation capability
The Smartcard interface supports the asynchronous protocol Smartcards as defined in the ISO standards
0.5, 1.5 stop bits for Smartcard operation
Single-wire half-duplex communication
Configurable multi buffer communication using DMA (direct memory access)
Buffering of received/transmitted bytes in reserved SRAM using centralized DMA
Separate enable bits for transmitter and receiver
Transfer detection flags
Receive buffer full
Transmit buffer empty
End of transmission flags

11. USART features (3/3) Parity control Four error detection flags
UART - Serial communic.
USART features (3/3)
4- 11
Parity control
Transmits parity bit
Checks parity of received data byte
Four error detection flags
Overrun error
Noise detection
Frame error
Parity error
Ten interrupt sources with flags
Multiprocessor communication - enter into mute mode if address match does not occur
Wake up from mute mode (by idle line detection or address mark detection)
Two receiver wakeup modes: Address bit (MSB, 9th bit), Idle line

12. UART - Serial communic.
4- 12
USART Block diagram
RM0090 figure 296

13. UART - Serial communic.
USART Register Map
4- 13

14. USART Status Register (USART_SR) (1010/1745 of RM0090)
ADC
3- 14
Address Offset : 0
TXE: Transmit data register empty
0: Data is not transferred to the shift register
1: Data is transferred to the shift register
RXNE: Read data register not empty
0: Data is not received
1: Received data is ready to be read.

15. USART Data Register (USART_DR) (1013/1745 of RM0090)
UART - Serial communic.
4- 15
Address Offset : 4
DR[8:0]: Data value

16. USART Baud Rate Register (USART_BRR) (1013/1745 of RM0090)
UART - Serial communic.
4- 16
Address Offset : 8
DIV_Mantissa[11:0]: mantissa of USARTDIV
DIV_Fraction[3:0]: fraction of USARTDIV

17. Fractional Baud Rate generator
UART - Serial communic.
4- 17
 Every baud rate generator has errors. Check the tolerance!
BRCLK: baud rate clock

18. ADC Control Register 1 (USART_CR1) (1013/1745 of RM0090)
3- 18
Address offset : 0x0C
UE: USART enable
0: USART pre-scaler and outputs disabled
1: USART enabled
M: Word length
0: 1 Start bit, 8 Data bits, n Stop bit
1: 1 Start bit, 9 Data bits, n Stop bit
TE: Transmitter enable
0: Transmitter is disabled
1: Transmitter is enabled
RE: Receiver enable
0: Receiver is disabled
1: Receiver is enabled and begins searching for a start bit

19. ADC Control Register 2 (ADC_CR2) (1016/1745 of RM0090)
3- 19
Address offset : 0x10
STOP[1:0]: STOP bits
00: 1 Stop bit
01: 0.5 Stop bit
10: 2 Stop bits
11: 1.5 Stop bit

20. ARM Peripheral Bus 2 access (APB2)
ADC
ARM Peripheral Bus 2 access (APB2)
2- 20
Reference: page 72/185 of “STM32F405xx STM32F407xx” “Datasheet – production data”

21. STM32F40x pin and ball definitions
ADC
STM32F40x pin and ball definitions
2- 21
Reference: page 45/185 of “STM32F405xx STM32F407xx” “Datasheet – production data”

22. Initialization of pin PA9 & PA10
ADC
Initialization of pin PA9 & PA10
3- 22
GPIOA Module
GPIO Mode Register (GPIOA_MODER)
Choose alternate function mode for the pin 9 (MODER9[1:0] = 0b10)
Choose alternate function mode for the pin 10 (MODER10[1:0] = 0b10)
GPIO alternate function low register (GPIOA_AFRH)
Select alternate function AF7 for the pin 9 (AFRL9[3:0] = 0b0111)
Select alternate function AF7 for the pin 10 (AFRL10[3:0] = 0b0111)
GPIO port pull-up/pull-down register (GPIOA_PUPDR)
Choose pull-up for the pin 9 (PUPDR9[1:0] = 0b01)
Choose pull-up for the pin 10 (PUPDR10[1:0] = 0b01)

23. Initialization of USART1
UART - Serial communic.
Initialization of USART1
4- 23
USART1 Module
USART1 Control Register 1 (USART1_CR1)
Enable the transmission and reception modes (TE = 0b1 & RE = 0b1)
Set the word length to 8 bits (M = 0b0)
Disable the parity control (PCE = 0b0)
USART2 Control Register 2 (USART1_ACR2)
Chose one stop bit (STOP[1:0] = 0b00)
USART1 Baud Rate Register (USART1_BRR)
Fix the baud rate at Baud (USART1_BRR[15:0] = 0x2D9)
Enable the USART1 (UE = 0b1)

24. Send & Receive a byte USART1 Module Send a byte Receive a byte
ADC
Send & Receive a byte
3- 24
USART1 Module
Send a byte
Wait until the USART1 is ready to send
TXE bit of USART1_SR
Write the byte to be send into USART1_DR
Receive a byte
Wait until the USART1 has received a byte
RXNE bit of USART1_SR
Read the received byte from USART1_DR