MCP2557FD datasheet(4/36 Pages) MICROCHIP

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MCP2557FD/8FD

DS20005533A-page 4

 2016 Microchip Technology Inc.

1.6

Mode Control

Figure 1-1 shows the state diagram of the MCP2557FD/

8FD.

1.6.1

UNPOWERED MODE (POR)

The MCP2557FD/8FD enters Unpowered mode if any

of the following conditions occur:

• After powering up the device

•If VDD drops below VPORL

•If VIO drops below VPORL_VIO

In Unpowered mode, the CAN bus will be biased to

ground using a high impedance. The MCP2557FD/

8FD is not able to communicate on the bus.

1.6.2

WAKE MODE

The MCP2557FD/8FD transitions from Unpowered

mode to Wake mode when VDD and VIO are above

their PORH levels. From Normal mode, if VDD is

smaller than VUVL, or if the bandgap output voltage is

not within valid range, the device will also enter Wake

mode.

In Wake mode, the CAN bus is biased to ground and

RXD is always high.

1.6.3

NORMAL MODE

When VDD exceeds VUVH, the band gap is within valid

range and TXD is High, the device transitions into

Normal mode. During POR, when the microcontroller

powers up, the TXD pin could be unintentionally pulled

down by the microcontroller powering up. To avoid

driving the bus during a POR of the microcontroller,

the transceiver proceeds to Normal mode only after

TXD is high.

In Normal mode, the driver block is operational and

can drive the bus pins. The slopes of the output

signals on CANH and CANL are optimized to reduce

Electromagnetic Emissions (EME). The CAN bus is

biased to VDD/2.

The high-speed differential receiver is active.

1.6.4

SILENT MODE

The device may be placed in Silent mode by applying

a high level to the ‘S’ pin (pin 8). In Silent mode, the

transmitter is disabled and the CAN bus is biased to

VDD/2. The high-speed differential receiver is active.

The CAN controller must put the MCP2557FD/8FD

back into Normal mode to enable the transmitter.

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