Datasheet

Product data sheet Rev. 1 — 23 October 2012 7 of 61

NXP Semiconductors

TJA1085

FlexRay active star coupler

6.4 Wake-up

The TJA1085 supports the following wake-up mechanisms:

• Remote wake-up via the bus (wake-up pattern or dedicated wake-up frame)

• Local wake-up via pin LWU

• Activity on the inner star interface (pins TRXD0 and TRXD1)

Any wake-up event will generate a WU interrupt. A remote wake-up on a branch will

generate an EVENT_BRx interrupt to indicate the branch where the wake-up pattern or

dedicated data frame was detected.

The host can identify the wake-up source by polling the General Status register

(WU_TRXD = 1 for a TRXD0/1 wake-up; WU_LOCAL = 1 for a local wake-up) and the

Branch Status register (WU_BRx = 1 for a remote wake-up).

6.4.1 Remote wake-up

When the TJA1085 is in AS_Standby or AS_Sleep, all branches are monitored for

wake-up events. When a valid wake-up pattern or data frame is detected on a branch, the

relevant WU_BRx status bit is set and the wake-up pattern/data frame is forwarded to all

other enabled branches.

A remote wake-up event occurring during an AS_Normal-to-AS_Standby or

AS_Normal-to-AS_Sleep transition will also be detected, setting the relevant WU_BRx

status bit and generating WU and EVENT_BRx interrupts.

6.4.1.1 Bus wake-up via wake-up pattern

A wake-up pattern consists of at least two consecutive wake-up symbols. A wake-up

symbol consists of a DATA_0 phase lasting longer than t

det(wake)DATA_0

, followed by an idle

phase lasting longer than t

det(wake)idle

, provided both wake-up symbols occur within a time

span of t

det(wake)tot

(see Figure 3). The transceiver also wakes up if the idle phases are

replaced by DATA_1 phases.

A wake-up event is not detected if an invalid wake-up pattern is received. See Ref. 1

for

more details on invalid wake-up patterns.