L99DZ100GP datasheet(92/197 Pages) STMICROELECTRONICS

92 / 197 page

Application information

L99DZ100G, L99DZ100GP

92/197

DS11546 Rev 5

When all SWRD_CRxx bits are set, SWEN can be set to enable the Selective Wakeup

function. In case SYSERR (SR 12) is set while Selective Wakeup is enabled, the Selective

Wakeup will be disabled automatically. In case SYSERR is set, enabling the Selective

Wakeup function is blocked. While selective wake-up is enabled (SWEN = 1), writing to

CR23 – CR29 is blocked but SWEN is reset to ‘0’. To re-configure the selective wakeup

feature, it is recommended to set SWEN = 0 before writing to CR23 - CR29.

Wake up from TRX SLEEP

If the CAN Transceiver is in TRX_Sleep state the CAN frame detection logic is disabled. The

wake up can be done in two steps. To enable the CAN frame detection logic a wake up

pattern must be sent on the bus. With the detection of the wake up pattern an automatic

state transition to TRX_BIAS State is done. WUP flag is set. In TRX_BIAS State the CAN

frame detection logic is enabled. If there is no bus communication for longer than tSilence an

automatic state transition to TRX_Sleep state will be done and the CAN frame detection

logic will be disabled. At frame error counter (FECNT_x) overflow, a wake up will be

performed and the selective wakeup feature will be disabled. For details, see Figure 31:

CAN transceiver state diagram.

4.10.5

CAN looping

If CAN_LOOP_EN (CR 2) is set the TxD_C input is mapped directly to the RxD_C pin. This

mode can be used in combination with the CAN Receive-only mode, to run diagnosis for the

CAN protocol handler of the micro controller.

4.10.6

Pretended networking

To support pretended networking concepts, the devices can be configured as follows:



V1_standby mode or Active mode (if watchdog is required)



Pretended Networking enabled (PNW_EN (CR 2) = 1)

In this configuration, the microcontroller is supplied by V1 in low current mode. The CAN

Automatic Voltage Biasing is active. Upon incoming CAN messages, the biasing is turned

on (TRX_BIAS State) and an interrupt is generated. If the device is in V1_standby mode it

remains in this mode.

The incoming CAN frames are passed to the microcontroller via the RxD_C signal line for

decoding.

4.10.7

CAN error handling

The devices provide the following four error handling features. After Power-on Reset (VS >

VPOR) the CAN transceiver is disabled. The transceiver is enabled by setting

CAN_GO_TRX_RDY(CR 1) = 1. The CAN transmitter will be disabled automatically in case

of the following errors:



Dominant TxD_C time out



CAN permanent recessive



RxD_C permanent recessive



Thermal Shutdown 1

The CAN receiver is not disabled in case of any failure condition.

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