MC68340 datasheet(363/441 Pages) FREESCALE

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MOTOROLA

MC68340 USER’S MANUAL

8- 19

STP—Stop bit

1 = Setting the STP bit stops all clocks within the timer module except for the clock

from the IMB. The clock from the IMB remains active to allow the CPU32 access

to the MCR. The clock stops on the low phase of the clock and remains stopped

until the STP bit is cleared by the CPU32 or a hardware reset. Accesses to timer

module registers while in stop mode produce a bus error. The timer module

should be disabled in a known state prior to setting the STP bit; otherwise,

unpredictable results may occur. The STP bit should be set prior to executing the

LPSTOP instruction to reduce overall power consumption.

0 = The timer operates in normal mode.

FRZ1, FRZ0—Freeze

These bits determine the action taken when the FREEZE signal is asserted on the IMB,

when the CPU32 has entered background debug mode. Table 8-2 lists the action taken

for each bit combination.

Table 8-2. FRZx Control Bits

FRZ1

FRZ0

ACTION

Ignore FREEZE

Reserved (FREEZE ignored)

Execution Freeze

Bits 12–8, 6–4—Reserved

SUPV—Supervisor/User

The value of this bit has no effect on registers permanently defined as supervisor-only

access.

1 = The timer registers defined as supervisor/user reside in supervisor data space

and are only accessible from supervisor programs.

0 = The timer registers defined as supervisor/user reside in user data space and are

accessible from either supervisor or user programs.

IARB3–IARB0—Interrupt Arbitration Bits

Each module that generates interrupts has an IARB field. These bits are used to

arbitrate for the bus in the case that two or more modules simultaneously generate an

interrupt at the same priority level. No two modules can share the same IARB value.

(Timer 1 and timer 2 should be programmed with different values if both are used.) The

reset value of the IARB field is $0, which prevents this module from arbitrating during

the interrupt acknowledge cycle. The system software should initialize the IARB field to

a value from $F (highest priority) to $1 (lowest priority).

Freescale Semiconductor, Inc.

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