Datasheet

TJA1085 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved.
Product data sheet Rev. 1 — 23 October 2012 6 of 61
NXP Semiconductors
TJA1085
FlexRay active star coupler
6. Functional description
6.1 Supply voltage
The TJA1085 state machine is adequately supplied if at least one of V
BAT
, V
CC
or V
BUF
is
available. The internal supply voltage to the state machine is denoted by V
DIG
. V
BUF
is an
auxiliary supply and is only needed for forwarding the wake-up pattern when V
CC
is not
available.
6.2 Host Control (HC) and Autonomous Power (AP) modes - APM flag
The APM flag determines whether the TJA1085 is host-controlled or is operating in
Autonomous Power mode. It is in AP mode by default.
The TJA1085 sets the APM flag:
• at power-on
• when a wake-up event is detected (on TXRD0/1, local or remote)
• when a V
CC
undervoltage event is detected in AS_Normal mode
• when a V
IO
undervoltage event lasts longer than t
to(uvd)(VIO)
The host can set or reset the APM flag at any time.
6.3 Signal router
The signal router transfers data received on an input channel to all channels configured as
outputs. If data is being received on more than one input channel at the same time, the
channel that was first to signal activity is selected and data on the other channel/s is
ignored. Whether or not the data on an output channel is transmitted depends on whether
the output channel is enabled or disabled.
The TJA1085 contains the following data input channels:
• Branches 1 to 4
• TRXD0/1 interface (inner star interface)
• TXD/TXEN interface
The TJA1085 contains the following data output channels:
• Branches 1 to 4
• TRXD0/1 interface
• RXD pin
6.3.1 TRXD collision
When the TRXD0/1 interface is configured as an output channel, a TRXD collision is
detected (COLL_TRXD = 1) if pins TRXD0 and TRXD1 are both LOW for longer than
t
det(col)(TRXD)
, generating a CLAMP_ERROR interrupt.
When a TRXD collision is detected, the TJA1085 transmits a DATA_0 to all other active
output channels (irrespective of the actual data on the selected input channel), until the
selected input channel detects idle state.