ATMEGA640 datasheet(248/436 Pages) MICROCHIP

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248

ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

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

TWEN must be set to enable the 2-wire Serial Interface, TWSTA must be written to one to transmit a START con-

dition and TWINT must be written to one to clear the TWINT Flag. The TWI will then test the 2-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 hardware, and the status code in TWSR will be 0x08 (see Table 24-2 on page 249). 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 0x18, 0x20, or 0x38. The

appropriate action to be taken for each of these status codes is detailed in Table 24-2 on page 249.

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 following value to TWCR:

This scheme is repeated until the last byte has been sent and the transfer is ended by generating a STOP condi-

tion 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:

After a repeated START condition (state 0x10) the 2-wire Serial Interface can access the same Slave again, or a

new Slave without transmitting a STOP condition. Repeated START enables the Master to switch between Slaves,

Master Transmitter mode and Master Receiver mode without losing control of the bus.

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

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