4 can controller timing modes – Rainbow Electronics AT91CAP9S250A User Manual

Page 706

706

6264A–CAP–21-May-07

AT91CAP9S500A/AT91CAP9S250A

Figure 39-18. Consumer Handling

39.7.4

CAN Controller Timing Modes

Using the free running

-bit internal timer, the CAN controller can be set in one of the two fol-

lowing timing modes:

• Timestamping Mode: The value of the internal timer is captured at each Start Of Frame or

each End Of Frame.

• Time Triggered Mode: The mailbox transfer operation is triggered when the internal timer

reaches the mailbox trigger.

Timestamping Mode is enabled by clearing the TTM bit in the CAN_MR register. Time Trig-
gered Mode is enabled by setting the TTM bit in the CAN_MR register.

39.7.4.1

Timestamping Mode

Each mailbox has its own timestamp value. Each time a message is sent or received by a
mailbox, the

-bit value MTIMESTAMP of the CAN_TIMESTP register is transferred to the

LSB bits of the CAN_MSRx register. The value read in the CAN_MSRx register corresponds
to the internal timer value at the Start Of Frame or the End Of Frame of the message handled
by the mailbox.

Figure 39-19. Mailbox Timestamp

MTCR

(CAN_MCRx)

MRDY

(CAN_MSRx)

CAN BUS

Remote Frame

Message x

Message y

(CAN_MDLx

CAN_MDHx)

MMI

(CAN_MSRx)

Remote Frame

Message x

TEOF

(CAN_MR)

MTIMESTAMP

(CAN_MSRx)

CAN_TIM

CAN BUS

MTIMESTAMP

(CAN_MSRy)

Message 1

Message 2

Start of Frame

TIMESTAMP

(CAN_TSTP)

End of Frame

Timestamp 1

Timestamp 2