ATmega88 datasheet(231/340 Pages) ATMEL

231 / 340 page

231

7530H–AVR–02/09

ATmega48/88/168 Automotive

Figure 19-19. Formats and States in the Slave Transmitter Mode

19.8.5

Miscellaneous States

There are two status codes that do not correspond to a defined TWI state, see Table 19-7.

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 2-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 2-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

Table 19-7.

Miscellaneous States

Status

Code

(TWSR)

Prescaler

Bits

are 0

Status of the 2-wire Se-

rial Bus and 2-wire Seri-

al Interface Hardware

Application Software Response

Next Action Taken by TWI Hardware

To/from

TWDR

To TWCR

TWI

0xF8

No relevant state infor-

mation

available;

TWINT = “0”

No TWDR ac-

tion

No TWCR action

Wait or proceed current transfer

0x00

Bus error due to an ille-

gal START or STOP

condition

No TWDR ac-

tion

Only the internal hardware is affected, no

STOP condition is sent on the bus. In all

cases, the bus is released and TWSTO is

cleared.

ATmega88 Datasheet(PDF) 231 Page - ATMEL Corporation

ATmega88 Datasheet(HTML) 231 Page - ATMEL Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL