ATmega32HVB datasheet(180/273 Pages) ATMEL

180 / 273 page

180

8042A–AVR–07/09

ATmega16HVB/32HVB

Figure 27-18. Formats and States in the Slave Transmitter Mode

27.7.5

Miscellaneous States

There are two status codes that do not correspond to a defined TWI state, see Table 27-6.

Status 0xF8 indicates that no relevant information is available because the TWINT flag is not

set. This occurs between other states, and when the TWI is not involved in a serial transfer.

Status 0x00 indicates that a bus error has occurred during a Two-wire Serial Bus transfer. A bus

error occurs when a START or STOP condition occurs at an illegal position in the format frame.

Examples of such illegal positions are during the serial transfer of an address byte, a data byte,

or an acknowledge bit. When a bus error occurs, TWINT is set. To recover from a bus error, the

TWSTO flag must set and TWINT must be cleared by writing a logic one to it. This causes the

TWI to enter the not addressed Slave mode and to clear the TWSTO flag (no other bits in TWCR

are affected). The SDA and SCL lines are released, and no STOP condition is transmitted.

SLA

DATA

$A8

$B8

$B0

Reception of the own

slave address and one or

more data bytes

Last data byte transmitted.

Switched to not addressed

slave (TWEA = '0')

Arbitration lost as master

and addressed as slave

From master to slave

From slave to master

Any number of data bytes

and their associated acknowledge bits

This number (contained in TWSR) corresponds

to a defined state of the Two-wire Serial Bus. The

prescaler bits are zero or masked to zero

P or S

DATA

$C0

DATA

$C8

P or S

All 1's

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