ATmega16 datasheet(181/315 Pages) ATMEL

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181

ATmega16(L)

2466E–AVR–10/02

Figure 86. 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 con-

dition as soon as the bus becomes free. After a START condition has been transmitted,

the TWINT flag is set by hardware, and the status code in TWSR will be $08 (See Table

73). 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 sta-

tus 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 73.

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 register. After updating TWDR, the TWINT bit should be cleared

(by writing it to one) to continue the transfer. This is accomplished by writing the follow-

ing value to TWCR:

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

generating a STOP condition or a repeated START condition. A STOP condition is gen-

erated 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

........

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