NRF9160-SICA-R7 datasheet(293/400 Pages) NORDIC

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Peripherals

ADDR

N-1

Stretch

Figure 91: TWI master writing data to a slave

The TWI master is stopped by triggering the STOP task. This task should be triggered during the

transmission of the last byte to secure that the TWI master will stop as fast as possible after sending the

last byte. The shortcut between LASTTX and STOP can alternatively be used to accomplish this.

Note: The TWI master does not stop by itself when the entire RAM buffer has been sent, or when

an error occurs. The STOP task must be issued, through the use of a local or PPI shortcut, or in

software as part of the error handler.

6.17.4 Master read sequence

A TWI master read sequence is started by triggering the STARTRX task. After the STARTRX task has been

triggered, the TWI master will generate a start condition on the TWI bus, followed by clocking out the

address and the READ/WRITE bit set to 1 (WRITE = 0, READ = 1). The address must match the address of

the slave device that the master wants to read from. The READ/WRITE bit is followed by an ACK/NACK bit

(ACK=0 or NACK = 1) generated by the slave.

After sending the ACK bit, the TWI slave will send data to the master using the clock generated by the

master.

Data received will be stored in RAM at the address specified in the RXD.PTR register. The TWI master

will generate an ACK after all but the last byte have been received from the slave. The TWI master will

generate a NACK after the last byte received to indicate that the read sequence shall stop.

A typical TWI master read sequence is illustrated in The TWI master reading data from a slave on page

294. Occurrence 2 in the figure illustrates clock stretching performed by the TWI master following a

SUSPEND task.

A SUSPENDED event indicates that the SUSPEND task has taken effect. This event can be used to

synchronize the software.

The TWI master will generate a LASTRX event when it is ready to receive the last byte, as shown in The

TWI master reading data from a slave on page 294. If RXD.MAXCNT > 1, the LASTRX event is generated

after sending the ACK of the previously received byte. If RXD.MAXCNT = 1, the LASTRX event is generated

after receiving the ACK following the address and READ bit.

The TWI master is stopped by triggering the STOP task. This task must be triggered before the NACK bit is

supposed to be transmitted. The STOP task can be triggered at any time during the reception of the last

byte. It is recommended to use the shortcut between LASTRX and STOP to accomplish this.

The TWI master does not stop by itself when the RAM buffer is full, or when an error occurs. The STOP

task must be issued, through the use of a local or PPI shortcut, or in software as part of the error handler.

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NRF9160-SICA-R7 Datasheet(PDF) 293 Page - Nordic Semiconductor