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AS8650

Datasheet - Detailed Descr i p ti on

7.13.10 Local Wake_up Flag

The Local Wake_up flag is set when the device detects a local wake-up request on WAKE pin. A local wake-up request is detected when a logic

state change on pin WAKE as shown in Figure 9. This indicates the microcontroller about the local wake event.

7.13.11 OVT_Warning Flag

7.13.12 OVT_Recover Flag

recovery levels.

7.13.13 Bus Failure Flags

The bus failure flag is set if the CAN Transceiver detects a bus line short-circuit condition to VSUP, V5V_LDO1 or GND. Such possible conditions

are indicated to microcontroller through these flags. All these flags are cleared on microcontroller read. If the fault condition still exist after

microcontroller read, the particular flag is set again. The device still be working in the current state. The microcontroller takes appropriate action

on reading of these flags.

current on pin CANH exceeds the threshold OC_CANH_th then the output OC_CANH switches on high level after a filter time t_OC_CANH.

current on pin CANH falls below the threshold LC_CANH_th then the output LC_CANH switches on high level after a filter time t_LC_CANH.

CANL exceeds the threshold OC_CANL_th, then the output OC_CANL switches on high level after a filter time t_OC_CANL.

current on pin CANL falls the threshold LC_CANL_th then the output LC_CANL switches on high level after a filter time t_LC_CANL.

7.13.14 Local Failure Flags

The AS8650 prevents the system from four kinds of local failures without disturbing the BUS network. The four failures are TxD dominant

clamping, RxD recessive clamping, TxD & RxD short, and bus dominant clamping. All these failures are indicated to microcontroller through

flags.

permanent dominant state, blocking BUS network communication. If pin TxD remains at a LOW level for longer than the TxD dominant time-out

network lock-up by disabling the transmitter of the Transceiver. The device will not change the functional state. The transmitter remains disabled

until the local failure flag is cleared by host command. The flag is cleared on microcontroller read.

see the bus dominant state and start sending message thinking bus is idle. This disturbs the BUS. This RxD recessive clamping is detected by

the device when BUS is at dominant state. On detection of this a failure RxD_Rec_Clamp flag is set and the transmitter is disabled. The flag is

cleared on microcontroller read. The transmitter is enabled by host command.

Transceiver receives a dominant signal, RxD outputs a dominant level. Because of the short circuit, TxD reflects a dominant signal, retaining the

dominant bus state. As a result TxD and the bus are clamped continuously dominant. The resulting effect is the same as for the continuously

clamped dominant TxD signal. The TxD dominant timeout interrupts the deadlock situation by disabling the transmitter and the TxD_RxD short

condition is differentiated. The bus becomes recessive again and TxD will be recessive if it is not driven by microcontroller. However, the failure

scenario may still exist and with the next dominant signal on the bus the described procedure will start again.

The device keeps the transmitter off after detection of TxD_RxD short fault and keeps updating this flag status. The microcontroller has to send

2 consecutive low pulses of duration 500ns with high period of 500ns in-between, in regular intervals to check short circuit recovery. This way a

local TxD/RxD short circuit will not disturb the communication of the remaining bus system.

even if there is no dominant transmitting node. The result may be a permanently dominant clamped bus. The device detects and reports a Bus

Dominant Clamping situation to microcontroller through BUS_Dom_Clamp flag. If the receiver detects a bus dominant phase of longer than the