STM8S datasheet(400/467 Pages) STMICROELECTRONICS

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Controller area network (beCAN)

RM0016

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23.8

Erroneous access to certain configuration registers can cause the hardware to temporarily

disturb the whole CAN network. Therefore the following registers can be modified by

software only while the hardware is in initialization mode:

CAN_BTR1, CAN_BTR2, CAN_FCR1, CAN_FCR2, CAN_FMR1, CAN_FMR2 and

CAN_DGR registers.

Although the transmission of incorrect data will not cause problems at the CAN network

level, it can severely disturb the application. A transmit mailbox can be only modified by

software while it is in empty state, refer to Figure 146: Transmit mailbox states.

The filters must be deactivated before their value can be modified by software. The

modification of the filter configuration (scale or mode) can be done by software only in

initialization mode.

23.9

Clock system

The clock tolerance limit as specified in CAN protocol is 1.58 % at speeds of up to 125

Kbps. For higher baud rates, it is suggested to use a crystal oscillator.

Note:

If the clock security system feature is enabled in the CLK controller (Refer to the description

of the CSSEN bit in the Clock security system register (CLK_CSSR) on page 97), there is a

way to put CAN automatically into the recessive state when a main clock failure occurs, so

that the CAN network does not get stuck by the device. However to ensure this, the PG0 I/O

pin must be configured in pull-up mode prior to using the beCAN. In this way, when a failure

occurs and the I/O alternate function is disabled, the line is pulled-up instead of floating.

23.10

beCAN low power modes

Note:

If a CAN frame is received in Wait, Halt or Active-halt modes, the microcontroller will be

woken-up but the CAN frame will be lost.

Table 68. beCAN behavior in low power modes

Mode

Description

Wait

No effect on beCAN, except that accesses to Tx/Rx mailboxes and filter values are not

possible (CPU clock is stopped).

beCAN interrupts cause the device to exit from WAIT mode.

Slow

No effect on beCAN.

Halt/ Active-

halt

BeCAN is halted. If the beCAN has been successfully put in Sleep mode (refer to

Section 23.4.3) before executing the halt instruction, any falling edge detected on

CAN_RX pin will trigger a beCAN Rx interrupt and wake-up the device from

Halt/Active-halt mode.

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