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32059L–AVR32–01/2012
AT32UC3B
19.13 Slave Mode
19.13.1
Definition
The Slave Mode is defined as a mode where the device receives the clock and the address from
another device called the master.
In this mode, the device never initiates and never completes the transmission (START,
REPEATED_START and STOP conditions are always provided by the master).
19.13.2
Application Block Diagram
Figure 19-23. Slave Mode Typical Application Block Diagram
19.13.3
Programming Slave Mode
The following fields must be programmed before entering Slave mode:
1. SADR (SMR): The slave device address is used in order to be accessed by master
devices in read or write mode.
2. MSDIS (CR): Disable the master mode.
3. SVEN (CR): Enable the slave mode.
As the device receives the clock, values written in CWGR are not taken into account.
19.13.4
Receiving Data
After a Start or Repeated Start condition is detected and if the address sent by the Master
matches with the Slave address programmed in the SADR (Slave ADdress) field, SVACC (Slave
ACCess) flag is set and SVREAD (Slave READ) indicates the direction of the transfer.
SVACC remains high until a STOP condition or a repeated START is detected. When such a
condition is detected, EOSACC (End Of Slave ACCess) flag is set.
19.13.4.1
Read Sequence
In the case of a Read sequence (SVREAD is high), TWI transfers data written in the THR (TWI
Transmit Holding Register) until a STOP condition or a REPEATED_START + an address differ-
ent from SADR is detected. Note that at the end of the read sequence TXCOMP (Transmission
Complete) flag is set and SVACC reset.
As soon as data is written in the THR, TXRDY (Transmit Holding Register Ready) flag is reset,
and it is set when the shift register is empty and the sent data acknowledged or not. If the data is
not acknowledged, the NACK flag is set.
Host with
TWI
Interface
TWD
TWCK
LCD Controller
Slave 1
Slave 2
Slave 3
RR
VDD
Host with TWI
Interface
Host with TWI
Interface
Master