at91sam9g20-cu ATMEL Corporation, at91sam9g20-cu Datasheet - Page 434

• Manufacturer Part Number: at91sam9g20-cu
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

31.9
31.9.1
31.9.2
31.9.3
31.9.4
31.9.4.1
434
Slave Mode
AT91SAM9G20 Preliminary
Definition
Application Block Diagram
Programming Slave Mode
Receiving Data
Read Sequence
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).
Figure 31-24. Slave Mode Typical Application Block Diagram
The following fields must be programmed before entering Slave mode:
As the device receives the clock, values written in TWI_CWGR are not taken into account.
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.
In the case of a Read sequence (SVREAD is high), TWI transfers data written in the TWI_THR
(TWI Transmit Holding Register) until a STOP condition or a REPEATED_START + an address
different from SADR is detected. Note that at the end of the read sequence TXCOMP (Transmis-
sion Complete) flag is set and SVACC reset.
As soon as data is written in the TWI_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.
1. SADR (TWI_SMR): The slave device address is used in order to be accessed by mas-
2. MSDIS (TWI_CR): Disable the master mode.
3. SVEN (TWI_CR): Enable the slave mode.
Host with
Interface
Master
ter devices in read or write mode.
TWI
TWD
TWCK
Host with TWI
Interface
Slave 1
Host with TWI
Interface
Slave 2
LCD Controller
Slave 3
R
6384B–ATARM–15-Dec-08
R
VDD