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Peripherals

The TWI slave can be forced to stop by triggering the STOP task. A STOPPED event will be generated when

the TWI slave has stopped. The TWI slave will clear the internal 'RX prepared' flag and go back to the IDLE

state when it has stopped, see also Terminating an ongoing TWI transaction on page 317.

The TWI slave will generate an ACK after every byte received from the master. The RXD.AMOUNT register

can be queried after a transaction to see how many bytes were received.

A typical TWI slave write command response is show in the following figure. Occurrence 2 in the figure

illustrates clock stretching performed by the TWI slave following a SUSPEND task.

ADDR

M-1

Stretch

Figure 101: The TWI slave responding to a write command

6.18.5 Master repeated start sequence

An example of a repeated start sequence is one in which the TWI master writes two bytes to the slave

followed by reading four bytes from the slave.

This is illustrated in the following figure.

In this example, the receiver does not know what the master wants to read in advance. This information

is in the first two received bytes of the write in the repeated start sequence. To guarantee that the CPU is

able to process the received data before the TWI slave starts to reply to the read command, the SUSPEND

task is triggered via a shortcut from the READ event generated when the read command is received. When

the CPU has processed the incoming data and prepared the correct data response, the CPU will resume

the transaction by triggering the RESUME task.

ADDR

Figure 102: Repeated start sequence

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NRF9160-SICA-R7 Datasheet(PDF) 316 Page - Nordic Semiconductor