ATmega16A datasheet(187/352 Pages) ATMEL

187 / 352 page

187

8154B–AVR–07/09

ATmega16A

Figure 20-11. Data Transfer in Master Transmitter Mode

A START condition is sent by writing the following value to TWCR:

TWEN must be set to enable the Two-wire Serial Interface, TWSTA must be written to one to

transmit a START condition and TWINT must be written to one to clear the TWINT Flag. The

TWI will then test the Two-wire Serial Bus and generate a START condition as soon as the bus

becomes free. After a START condition has been transmitted, the TWINT Flag is set by hard-

ware, and the status code in TWSR will be $08 (See Table 20-2). In order to enter MT mode,

SLA+W must be transmitted. This is done by writing SLA+W to TWDR. Thereafter the TWINT bit

should be cleared (by writing it to one) to continue the transfer. This is accomplished by writing

the following value to TWCR:

When SLA+W have been transmitted and an acknowledgement bit has been received, TWINT is

set again and a number of status codes in TWSR are possible. Possible status codes in Master

mode are $18, $20, or $38. The appropriate action to be taken for each of these status codes is

detailed in Table 20-2.

When SLA+W has been successfully transmitted, a data packet should be transmitted. This is

done by writing the data byte to TWDR. TWDR must only be written when TWINT is high. If not,

the access will be discarded, and the Write Collision bit (TWWC) will be set in the TWCR Regis-

ter. After updating TWDR, the TWINT bit should be cleared (by writing it to one) to continue the

transfer. This is accomplished by writing the following value to TWCR:

This scheme is repeated until the last byte has been sent and the transfer is ended by generat-

ing a STOP condition or a repeated START condition. A STOP condition is generated by writing

the following value to TWCR:

A REPEATED START condition is generated by writing the following value to TWCR:

TWCR

TWINT

TWEA

TWSTA

TWSTO

TWWC

TWEN

–

TWIE

Value

TWCR

TWINT

TWEA

TWSTA

TWSTO

TWWC

TWEN

–

TWIE

Value

TWCR

TWINT

TWEA

TWSTA

TWSTO

TWWC

TWEN

–

TWIE

Value

TWCR

TWINT

TWEA

TWSTA

TWSTO

TWWC

TWEN

–

TWIE

Value

TWCR

TWINT

TWEA

TWSTA

TWSTO

TWWC

TWEN

–

TWIE

Value

Device 1

MASTER

TRANSMITTER

Device 2

SLAVE

RECEIVER

Device 3

Device n

SDA

SCL

........

ATmega16A 데이터시트(PDF) 187 Page - ATMEL Corporation

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