33742 datasheet(37/70 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33742

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

CAN PHYSICAL INTERFACE

The SBC features a high-speed CAN physical interface for bus communication from 60kbps up to 1.0Mbps. Figure 19 is a

simplified block diagram of the CAN interface of the 33742.

Figure 19. Simplified Block Diagram of CAN Interface

CAN INTERFACE SUPPLY

The supply voltage for the CAN transceiver is the V2 pin.

The CAN interface also has a supply path from the external

supply line through the VSUP pin. This path is used in CAN

Sleep mode to allow wake-up detection.

During CAN communication (transmission and reception),

the CAN interface current is sourced from the V2 pin. During

CAN low power mode, the current is sourced from the VSUP

pin.

MAIN OPERATION MODES DESCRIPTION

The CAN interface of the SBC has two main operating

modes: TXRX and Sleep mode. The modes are controlled by

the CAN SPI Register. In the TXRX mode, which is used for

communication, four different slew rates are available for the

user. In the Sleep mode, the user has the option of enabling

or disabling the remote CAN wake-up capability.

CAN DRIVER OPERATION IN TXRX MODE

When the CAN interface is in TXRX mode, the driver has

two states: recessive or dominant. The driver state is

controlled by the TXD pin. The bus state is reported through

the RXD pin.

When TXD is HIGH, the driver is set in recessive state, and

CANH and CANL lines are biased to the voltage set at V2

divided by 2, or approximately 2.5V.

When TXD is LOW, the bus is set into dominant state:

CANL and CANH drivers are active. CANL is pulled to

ground, and CANH is pulled HIGH toward 5.0V (voltage at

V2).

The RXD pin reports the bus state: CANH minus CANL

voltage is compared versus an internal threshold (a few

hundred millivolts). If CANH minus CANL is below the

threshold, the bus is recessive and RXD is set HIGH. If CANH

minus CANL is above the threshold, the bus is dominant and

RXD is set LOW. This is illustrated in Figure 19.

Bus Termination (60

Ω)

CANH Line

CANL Line

TXD

RXD

Differential

Receiver

Driver

2.5 V

Wake-up

Receiver

Pattern

Recognition

Internal

VSUP

Wake-up

Signal

CANH

CANL

SPI Control

33742

33742 Datasheet(PDF) 37 Page - Freescale Semiconductor, Inc

33742 Datasheet(HTML) 37 Page - Freescale Semiconductor, Inc

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