AT89LP6440 datasheet(120/194 Pages) ATMEL

120 / 194 page

120

3706A–MICRO–9/09

AT89LP6440 - Preliminary

TWEN must be written to one to enable the TWI. The AA bit must be written to one to enable the

acknowledgment of the device’s own slave address or the general call address. STA and STO

must be written to zero.

When TWAR and TWCR have been initialized, the TWI waits until it is addressed by its own

slave address (or the general call address if enabled) followed by the data direction bit. If the

direction bit is “0” (write), the TWI will operate in SR mode, otherwise ST mode is entered. After

its own slave address and the write bit have been received, the TWIF flag is set and a valid sta-

tus code can be read from TWSR. The status code is used to determine the appropriate

software action. The appropriate action to be taken for each status code is detailed in Table 18-

8. The Slave Receiver mode may also be entered if arbitration is lost while the TWI is in the Mas-

ter mode (see states 68h and 78h).

If the AA bit is reset during a transfer, the TWI will return a “Not Acknowledge” (“1”) to SDA after

the next received data byte. This can be used to indicate that the slave is not able to receive any

more bytes. While AA is zero, the TWI does not acknowledge its own slave address. However,

the Two-wire Serial Bus is still monitored and address recognition may resume at any time by

setting AA. This implies that the AA bit may be used to temporarily isolate the TWI from the Two-

wire Serial Bus.

Table 18-8.

Status Codes for Slave Receiver Mode

Status

Code

(TWSR)

Status of the Two-wire

Serial Bus and Two-wire

Serial Interface Hardware

Application Software Response

Next Action Taken by TWI Hardware

To/from TWDR

To TWCR

STA

STO

TWIF

60h

Own SLA+W has been

received; ACK has been

returned

No action

Data byte will be received and NOT ACK will be

returned

No action

Data byte will be received and ACK will be

returned

68h

Arbitration lost in SLA+R/W

as master; own SLA+W has

been received; ACK has

been returned

No action

Data byte will be received and NOT ACK will be

returned

No action

Data byte will be received and ACK will be

returned

70h

General call address has

been received; ACK has

been returned

No action

Data byte will be received and NOT ACK will be

returned

No action

Data byte will be received and ACK will be

returned

78h

Arbitration lost in SLA+R/W

as master; General call

address has been received;

ACK has been returned

No action

Data byte will be received and NOT ACK will be

returned

No action

Data byte will be received and ACK will be

returned

80h

Previously addressed with

own SLA+W; data has been

received; ACK has been

returned

Read data byte

Data byte will be received and NOT ACK will be

returned

Read data byte

Data byte will be received and ACK will be

returned

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