L9965T datasheet(40/62 Pages) STMICROELECTRONICS

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Procedure 2: Burst request from transceiver A and response from transceiver B, when the pointer of transceiver

B already points to the RX FIFO

1. Send an SPI burst request to the target device along the chain through one of the two transceivers in the

chain (see Section 5.8.2.2).

2. Wait to receive the N response frames to the burst.

3. From transceiver B, send one frame to pop from the FIFO the burst request sent by transceiver A.

4. From transceiver B, send N frames to pop from the FIFO the related N responses of burst.

Procedure 3: Burst request from transceiver A and response from transceiver B, when the pointer of transceiver

B points to its internal register

1. Send an SPI burst request to the target device along the chain through one of the two transceivers in the

chain (see Section 5.8.2.2).

2. Wait to receive the N response frames to the burst.

3. From transceiver B, send a FIFO pop frame to point to the FIFO memory (the MISO will contain the data of the

internal register read before).

4. From transceiver B, send one SPI frame to pop from the FIFO the burst request sent by transceiver.

5. From transceiver B, send N SPI frames to pop from the FIFO the related N responses of burst.

5.8.2.6

Chained devices wakeup requested by MCU

The wakeup of the devices on the VIF bus requested by MCU is an asynchronous event with respect to the

CYCLIC_WAKEUP thread managed in background by the L9965T/TS.

Figure 16 shows a typical application scenario where the MCU wakes up the daisy-chain that was previously

operating in CYCLIC_WAKEUP mode.

To wake up the daisy-chain:

1. The MCU moves both L9965T channels to NORMAL state

2. The MCU waits for the L9965T wakeup period (TWAKEUP)

3. The MCU checks the internal status bit of both L9956T channels (WAKEUP_CYCLIC_TRX_SENDER,

WAKEUP_CYCLIC_TRX_LISTENER in register GEN_STATUS2) to determine which one is operating in

SENDER mode, and sends it a SPI FAULT/WAKEUP command (see par 5.8.3.1) to be propagated on the VIF.

This guarantees that CYCLIC_WAKEUP and FAULT/WAKEUP tones travel in the same direction to avoid

conflicts.

4. The listener channel of the transceiver, receiving the FAULT/WAKEUP tone from the VIF, assert the FLT pin.

5. Waking up the whole daisy chain will take approximately NVIF_STACK*TVIF_WAKEUP_TIME, and is confirmed by

the FLT interrupt generated by the listener L9965T channel, once it receives the FAULT/WAKEUP tone

a. The MCU is supposed to check the L9965T status register to verify that the FLT/WAKEUP source flag is

asserted. As shown in Figure 12, it is possible that a CYCLIC_WAKEUP tone reaches the LISTENER

transceiver before the FAULT/WAKEUP tone arrives. In such case, the MCU shall anyway wait for the

FAULT/WAKEUP tone to consider the daisy-chain fully woken up.

L9965T/L9965TS

Functional description

DS14987 - Rev 1

page 40/62

L9965T Datasheet(PDF) 40 Page - STMicroelectronics