Programming Microcontroller USART Universal Synchronous/Asynchronous Receiver Transmitter

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UART - Serial communic.

Programming MicrocontrollerUSART

Universal Synchronous/Asynchronous Receiver Transmitter

Autumn 2012

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UART - Serial communic. Typical serial communication(low level)

Full-duplex interface

Device 1(Data Set)

Device 2(Data Terminal)

-PC-Embedded system

-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

Transmit

ReceiveTransmit

Receive

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UART - Serial communic. RS-232-C pin assignmentsD-Sub male on PC

PinDB9

PinDB25

Symbol Direction

Text

Out

In

1 8 DCD Data Carrier Detect

2 3 Rx Receive Data

3 2 Tx Transmit Data

4 20 DTR Data Terminal Ready

5 7 Gnd Signal Ground

6 6 DSR Data Set Ready

7 4 RTS Request to Send

8 5 CTS Clear to Send

9 22 RI Ring IndicatorRS-232-C: Radio Sector, American Standard since 1969sEIA: Electronic Industry Alliance

Male -> SteckerFemale -> Buchse

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UART - Serial communic. Serial data format(logical representation)

5-8 data bits

Parity bit if enabled

1-2 stop bitsmsblsb

start

1

n0

time

lsb: least significant bit (20)msb: most significant bit (2 db-1)

1 bit time = 1 / baud rate

Example: parity enabled, 2 stop bits

Normally one Byte is sent as 8 data bitsOr: One Byte is sent as 7 data bits + parity

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UART - Serial communic. Hyperterminal usage

Start -> Zubehör -> Kommunikation -> HyperterminalGo offlineConfigure COM-Port: File->Properties

Xon/Xoff: Software handshake (Exchange on..)<ctrl-q>/<ctrl-s>

both sides must implement thissoftware handshake. The senderhas to stop almost immediatelyupon reception of Xoff characterBinary data transmission is notpossible.

Hardware: RTS/CTS hardware handshakeguarantees loss-free transmissionon a byte level and allows binary data transmission

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UART - Serial communic. UART – What is it good for?

Simple serial communication (3-wire) Multiple physical interfaces:

EIA-232 Peer-to-peer (former RS-232-C 1969). Gnd based (-15..-3,3..15 V)

EIA-485 Party Line, multi-point link (SCSI, ISDN, ... EIA-422 : Balanced lines, no ground link (D+/D-) on drivers up to

1'000m @ 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

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

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UART - Serial communic. Hardware flow control

nRTS will be switched on and off by programmable receiver DMA watermarks

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UART - Serial communic. UART features (1/3)

Full duplex, asynchronous communications NRZ standard format (Mark/Space) Fractional baud rate generator systems

A common programmable transmit and receive baud rates up to 4.5 MBits/s Programmable data word length (8 or 9 bits) Configurable stop bits - support for 1 or 2 stop bits LIN (Local Interconnection Network) Master Synchronous Break send

capability and LIN slave break detection capability 13-bit break generation and 10/11 bit break detection when USART is

hardware configured for LIN Transmitter clock output for synchronous transmission IrDA SIR Encoder Decoder

Support for 3/16 bit duration for normal mode Smartcard Emulation Capability

The Smartcard interface supports the asynchronous protocol Smartcards as defined in ISO 7816-3 standards

0.5, 1.5 Stop Bits for Smartcard operation

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UART - Serial communic. UART features (2/3)

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

Parity control Transmits parity bit Checks parity of received data byte

Four error detection flags Overrun error Noise error Frame error Parity error

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UART - Serial communic. UART features (3/3)

Ten interrupt sources with flags: CTS changes LIN break detection Transmit data register empty Transmission complete Receive data register full Idle line received Overrun error Framing error Noise error Parity error

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

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UART - Serial communic.

UA

RT B

lock

d

iag

ram

Ref. RM0008 Reference manual, figure 277

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UART register boundary addresses4- 13

UART - Serial communic.

Ref. RM0008 Reference Manual, table 3

Boundary address Peripheral Bus

0x4000_4400 – 0x4000_47FF USART2 APB1

0x4000_4800 – 0x4000_4BFF USART3 APB1

0x4000_4C00 – 0x4000_4FFF USART4 APB1

0x4000_5000 – 0x4000_53FF USART5 APB1

0x4001_3800 – 0x4001_3BFF USART1 APB2

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UART - Serial communic. UART register offset addresses

Ref. RM0008 Reference Manual, table 198

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UART - Serial communic. UART register description (1/4)

Status register (USART_SR)

CTS: Clear to send TXE: Transmit data register empty TC: Transmission complete RXNE: Read data register not empty NE: Noise error FE: Frame error PE: Parity error

Data register (USART_DR) Contains the received or transmitted data character, depending it

is read from or written to

Ref. RM0008 Reference Manual, chapter 27.6

MS_uC / fue1 / V01UART register description (2/4)

Control register 1 (USART_CR1)

UE: USART enable M: Word length PCE: Parity control enable PS: Parity selection PEIE: Parity interrupt enable TXEIE: TXE interrupt enable TCIE: Transmission complete interrupt enable RXNEIE: RXNE interrupt enable TE: Transmitter enable RE: Receiver enable

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UART - Serial communic.

MS_uC / fue1 / V01 UART register description (3/4)

Control register 2 (USART_CR2)

STOP: Stop bits CLKEN: Clock enable CPOL: Clock polarity CPHA: Clock phase

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UART - Serial communic.

MS_uC / fue1 / V01UART register description (4/4)

Control register 3 (USART_CR3)

CTSIE: CTS interrupt enable CTSE: CTS enable RTSE: RTS enable DMAT: DMA enable transmitter DMAR: DMA enable receiver HDSEL: Half-duplex selection EIE: Error interrupt enable

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UART - Serial communic.

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UART - Serial communic. Fractional Baud Rate generator

The Baud rate for the receiver and transmitter (Rx & Tx) are both set to the same value

USARTDIV is an unsigned fixed point number that is coded on the USART_BRR register

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Error calculation for programmed baud rates4- 20

UART - Serial communic.

Ref. RM0008 Reference Manual, table 192

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UART - Serial communic. Pin connections of USART2RM0008 Reference manual, Table 53

USART2 port functional description PD5: Alternate push-pull PD6: Input floating

USART2 port remap PD5 USART_TX PD6 USART_RX