ST72561 datasheet(174/262 Pages) STMICROELECTRONICS

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ST72561

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beCAN CONTROLLER (Cont’d)

Figure 96. beCAN Operating Modes

10.9.3 Operating Modes

The beCAN has three main operating modes: ini-

tialization, normal and sleep. After a hardware

reset, beCAN is in sleep mode to reduce power

consumption. The software requests beCAN to

enter initialization or sleep mode by setting the

INRQ or SLEEP bits in the CMCR register. Once

the mode has been entered, beCAN confirms it by

setting the INAK or SLAK bits in the CMSR regis-

ter. When neither INAK nor SLAK are set, beCAN

is in normal mode. Before entering normal mode

beCAN always has to synchronize on the CAN

bus. To synchronize, beCAN waits until the CAN

bus is idle, this means 11 consecutive recessive

bits have been monitored on CANRX.

10.9.3.1 Initialization Mode

The software initialization can be done while the

hardware is in Initialization mode. To enter this

mode the software sets the INRQ bit in the CMCR

firmed the request by setting the INAK bit in the

CMSR register.

To leave Initialization mode, the software clears

the INQR bit. beCAN has left Initialization mode

once the INAK bit has been cleared by hardware.

While in Initialization mode, all message transfers

to and from the CAN bus are stopped and the sta-

tus of the CAN bus output CANTX is recessive

(high).

Entering Initialization Mode does not change any

of the configuration registers.

To initialize the CAN Controller, software has to

set up the Bit Timing registers and the filter banks.

If a filter bank is not used, it is recommended to

leave it non active (leave the corresponding FACT

bit cleared).

10.9.3.2 Normal Mode

Once the initialization has been done, the software

must request the hardware to enter Normal mode,

to synchronize on the CAN bus and start reception

and transmission. Entering Normal mode is done

by clearing the INRQ bit in the CMCR register and

waiting until the hardware has confirmed the re-

quest by clearing the INAK bit in the CMSR regis-

ter. Afterwards, the beCAN synchronizes with the

data transfer on the CAN bus by waiting for the oc-

currence of a sequence of 11 consecutive reces-

sive bits (

≡ Bus Idle) before it can take part in bus

activities and start message transfer.

The initialization of the filter values is independent

from Initialization mode but must be done while the

filter bank is not active (corresponding FACTx bit

cleared). The filter bank scale and mode configu-

ration must be configured in initialization mode.

SLEEP

SYNC

INITIALIZATION

NORMAL

P *

INR

INRQ

RESET

SLAK= 1

INAK = 0

SLAK= X

INAK = X

SLAK= 0

INAK = 1

SLE

SLAK= 0

INAK = 0

INRQ

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