Rainbow-electronics ATmega8515L Bedienungsanleitung PDF herunterladen (Seite 150)

150

ATmega8515(L)

2512A–AVR–04/02

Read Access Doing a read access to the UBRRH or the UCSRC Register is amore complex opera-

tion. However, in mostapplications, it israrely necessary to read any of these registers.

The read access iscontrolledbyatimedsequence. Reading the I/Olocation once

returns the UBRRH Registercontents. If the registerlocation wasread in previous sys-

tem clock cycle,reading the register in the current clock cycle will returnthe UCSRC

contents. Note that thetimedsequence forreading the UCSRC is an atomic operation.

Interrupts musttherefore be controlled(e.g.,bydisabling interrupts globally) during the

read operation.

The following codeexample shows how to read the UCSRC Registercontents.

Note: 1. Theexample codeassumes that the part specificheaderfileis included.

Theassembly codeexample returns the UCSRC value in r16.

Reading the UBRRHcontents is not an atomic operation and thereforeitcan be read as

an ordinary register, aslong as the previous instruction did not access the register

location.

USART Register

Description

USART I/O Data Register –

UDR

The USART Transmit Data Bufferregister andUSART Receive Data Buffer Registers

sharethe same I/O address referred to asUSART Data Register orUDR. TheTransmit

Data Buffer Register(TXB) will bethe destination fordata writtentothe UDR Register

location. Reading the UDR Registerlocation will returnthe contents of theReceive Data

Buffer Register(RXB).

For 5-, 6-, or7-bit characters theupper unusedbitswill beignoredbytheTransmitter

andset to zero by theReceiver.

Assembly Code Example

(1)

USART_ReadUCSRC:

;

Read UCSRC

in r16,UBRRH

in r16,UCSRC

ret

CCode Example

(1)

unsigned char USART_ReadUCSRC( void )

{

unsigned char ucsrc;

Read UCSRC

ucsrc = UBRRH;

ucsrc = UCSRC;

return ucsrc;

}

Bit 76543 210

RXB[7:0] UDR (Read)

TXB[7:0] UDR (Write)

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

1 2 ... 145 146 147 148 149 150 151 152 153 154 155 ... 222 223

Kommentare zu diesen Handbüchern

Keine Kommentare

Rainbow-electronics ATmega8515L Bedienungsanleitung Seite 150

Kommentare zu diesen Handbüchern

Verwandte Produkte und Handbücher für Sensoren Rainbow-electronics ATmega8515L