AS8221

Datasheet - Detailed Descr i p ti on

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Revision 1.4

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8 Detailed Description

The AS8221 is a FlexRay Transceiver operating as an interface between the Communication Controller and the wired bus lines. The AS8221 is

designed to extend the application range for high speed and safety critical time triggered bus systems in an automotive environment. The drivers

are short circuit protected against the positive and negative supply voltage to increase the robustness and reliability of automotive systems. The

AS8221 operates at baudrates up to 10 Mbps.

8.1 Block Description

The AS8221 consists of 9 functional blocks (see Figure 1):

8.2 Events

Transitions in order to change between the operation modes are possible only if events are detected. The device supports three type of events,

events on the host controller interface (STBN, EN), detection of undervoltage or supply voltage recovery and wake events. Mode changes are

only performed upon detected events.

8.3 Operating Modes

The AS8221 provides the following operating modes:

NORMAL: non-low-power mode

RECEIVE-ONLY: non-low-power mode

STANDBY: low-power mode

GO-TO-SLEEP: low-power mode

SLEEP: low-power mode

Table 4. Functional Blocks

Functional Block

Short Description

Host Controller Interface (HCI)

Digital interface between the Transceiver and the host controller (HC)

The host interface comprises the read-out handler, which delivers failure and status

information via the ERRN pin to the host controller.

Communication Controller Interface (CCI)

Digital interface between the Transceiver and the FlexRay communication controller

(CC)

Bus Guarding Interface (BGI)

Digital interface between the Transceiver and the FlexRay bus guardian (BG) or

monitoring circuitry.

Power Supply Interface

(PSI)

The power supply interface consists of the voltage monitor (VM) with two analog

inhibit outputs switching external voltage supplies.

Internal Logic (IL)

The digital signals from the functional blocks of the device are fed into the internal

logic where the forwarding of FlexRay messages from analog side to digital interfaces

and vice versa is done. The state machine is embedded in the Internal Logic and the

handling of error, wake, and power-on flags is executed herein.

Bus Failure Detector (BFD)

Temperature Protection (TP)

The bus failure detector is directly connected to the bus pins, in order to detect several

external failure conditions which may occur on the bus.

The temperature protection turns off the output driver when reaching the specified

internal temperature in order to protect the device.

Transmitter

The transmitter provides the differential signalling according the FlexRay standard on

the bus pins.

Receiver

The Receiver captures FlexRay valid signals at the bus pins and provides the

received data streams to the Internal Logic.

Wake-Up Detector (WUD)

The wake-up detector recognizes valid wake-up frames on the bus, recognizes a

wake signal on the local WAKE pin and signals valid wake-up events to the Internal

Logic.