L9788 datasheet(149/264 Pages) STMICROELECTRONICS

149 / 264 page

DS12308 Rev 4

149/264

L9788

CAN FD interface

263

12.3

CAN normal mode

If CAN_EN bit MSC_CONFIG-REG17-1[2] is set and the U-chip is in ON state the CAN

transceiver is in normal mode (referring to state diagram, CAN_RX or CAN_TRX state). In

this state the transmitter and receiver can be configured by MSC (CAN_TX_EN,

CAN_RX_EN) as follows:



TRX Standby: transmitter disabled and CAN_RX pin masked to 1(CAN_TX_EN = '0',

CAN_RX_EN = '0');



TRX Listen: transmitter disabled, receiver enabled (CAN_TX_EN = '0', CAN_RX_EN =

'1');



TRX transmit: transmitter enabled CAN_RX pin masked to 1 (CAN_TX_EN = '1',

CAN_RX_EN = '0');



TRX Normal (default): transmitter enabled receiver enabled (CAN_TX_EN = '1',

CAN_RX_EN = '1')

In normal mode the CAN biasing is always active

Wake up by CAN disabled option is allowed only for the application that does not require the

transceiver (CANH/L not connected to any bus).

12.4

CAN low-power mode

When L9788 is ON it is possible to deactivate the CAN transceiver setting the MSC bit

CAN_EN (MSC_CONFIG-REG17_1[2]) to zero, sending the CAN in Low-power Mode. The

CAN transceiver remains deactivated until it will be activated again setting the CAN_EN bit.

When L9788 is OFF the CAN transceiver is always in Low-power Mode independently from

any other configuration bit except CAN_WAKEUP_EN, which if set to zero, sends it to Sleep

mode once the transceiver goes to CAN_STBY_OFF state. In Low-power mode the biasing

can be active or inactive depending on CAN_AUTO_BIAS bit value and from the CAN bus

activity (see state diagram), furthermore the transmitter is always disabled and the CAN_RX

pin is always masked to recessive. When biasing is disabled the receiver input termination

will be biased at zero volt.

12.5

CAN Sleep Mode

When the CAN transceiver goes in CAN_STBY_OFF with CAN_WAKEUP_EN = '0' it falls in

an ultra low current consumption state called Sleep mode. In this state for the L9788 is

impossible to detect Wake-up activity on CAN bus and consequently no power-up is done

for a CAN detection (pattern or no pattern).

12.6

CAN error handling

CAN Driver HS and LS are supplied by a dedicated pin (VDD_CAN) to avoid disturbances

of CAN activity on main supply lines. After internal power on reset of VB_STBY the CAN

transceiver is configured according to the configuration register bit default values. When the

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