Motorola MCF5281, MCF5282 user manual General Purpose Timers Gpta and Gptb, FlexCAN

Functional Description

7.3.2.22General Purpose Timers (GPTA and GPTB)

When not stopped, the General Purpose Timers may generate an interrupt to exit the low-power modes.

Clearing the timer enable bit (TE) in the GPT system control register 1 (GPTSCR1) or the pulse accumulator enable bit (PAE) in the GPT pulse accumulator control register (GPTPACTL) disables timer functions. Timer and pulse accumulator registers are still accessible by the CPU and BDM interface, but the remaining functions of the timer are disabled.

The timer is unaffected by either the wait or doze modes and may generate an interrupt to exit these modes.

In stop mode, the General Purpose Timers stop immediately and freeze their operation, register values, state machines, and external pins. Upon exiting stop mode, the timer will resume operation unless stop mode was exited by reset.

7.3.2.23FlexCAN

When enabled, the FlexCAN module is capable of generating interrupts and bringing the device out of a low-power mode. The module has 35 interrupt sources (32 sources due to message buffers and 3 sources due to Bus-off, Error and Wake-up).

When in stop mode, a recessive to dominant transition on the CAN bus causes the WAKE-INT bit in the error & status register to be set. This event can cause a CPU interrupt if the WAKE-MASK bit in module configuration register (MCR) is set.

When setting stop mode in the FlexCAN (by setting the MCR[STOP] bit), the FlexCAN checks for the CAN bus to be either idle or waits for the third bit of intermission and checks to see if it is recessive. When this condition exists, the FlexCAN waits for all internal activity other than in the CAN bus interface to complete and then the following occurs:

•The FlexCAN shuts down its clocks, stopping most of the internal circuits, to achieve maximum possible power saving.

•The internal bus interface logic continues operation, enabling CPU to access the MCR register.

•The FlexCAN ignores its Rx input pin, and drives its Tx pins as recessive.

•FlexCAN loses synchronization with the CAN bus, and STOP_ACK and NOT_RDY bits in MCR register are set.

Exiting stop mode is done in one of the following ways:

•Reset the FlexCAN (either by hard reset or by asserting the SOFT_RST bit in MCR).

•Clearing the STOP bit in the MCR.

MOTOROLA Chapter 7. Power Management 7-13