Atmel SAM9X25, Manual

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11054A–ATARM–27-Jul-11
SAM9X25
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11054A–ATARM–27-Jul-11
SAM9X25
Note that a STOP or a repeated START always follows a NACK.
See Figure 38-25 on page 772 .
38.10.4.2 Write Sequence
In the case of a Write sequence (SVREAD is low), the RXRDY (Receive Holding Register
Ready) flag is set as soon as a character has been received in the TWI_RHR (TWI Receive
Holding Register). RXRDY is reset when reading the TWI_RHR.
TWI continues receiving data until a STOP condition or a REPEATED an address dif-
ferent from SADR is detected. Note that at the end of the write sequence TXCOMP flag is set
and SVACC reset.
See Figure 38-26 on page 772 .
38.10.4.3 Clock Synchronization Sequence
In the case where TWI_THR or TWI_RHR is not written/read in time, TWI performs a clock
synchronization.
Clock stretching information is given by the SCLWS (Clock Wait state) bit.
See Figure 38-28 on page 774 and Figure 38-29 on page 774 .
38.10.4.4 General Call
In the case where a GENERAL CALL is performed, GACC (General Call ACCess) flag is set.
After GACC is set, it is up to the programmer to interpret the meaning of the GENERAL CALL
and to decode the new address programming sequence.
See Figure 38-27 on page 773 .
38.10.4.5 DMAC
As it is impossible to know the exact number of data to receive/send, the use of DMAC is NOT
recommended in SLAVE mode.
38.10.5 Data Transfer
38.10.5.1 Read Operation
The read mode is defined as a data requirement from the master.
After a START or a REPEATED START condition is detected, the decoding of the address
starts. If the slave address (SADR) is decoded, SVACC is set and SVREAD indicates the direc-
tion of the transfer.
Until a STOP or REPEATED START condition is detected, TWI continues sending data loaded
in the TWI_THR register.
If a STOP condition or a REPEATED START + an address different from SADR is detected,
SVACC is reset.
Figure 38-25 on page 772 describes the write operation.