MC68331TS datasheet(19/84 Pages) FREESCALE

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MC68331TS/D

SWP —Software Watchdog Prescale

This bit controls the value of the software watchdog prescaler.

0 = Software watchdog clock not prescaled

1 = Software watchdog clock prescaled by 512

SWT[1:0] —Software Watchdog Timing

This field selects the divide ratio used to establish software watchdog time-out period. The following ta-

ble gives the ratio for each combination of SWP and SWT bits.

HME —Halt Monitor Enable

0 = Disable halt monitor function

1 = Enable halt monitor function

BME —Bus Monitor External Enable

0 = Disable bus monitor function for an internal to external bus cycle.

1 = Enable bus monitor function for an internal to external bus cycle.

BMT[1:0] —Bus Monitor Timing

This field selects a bus monitor time-out period as shown in the following table.

3.2.3 Bus Monitor

The internal bus monitor checks for excessively long DSACK response times during normal bus cycles

and for excessively long DSACK or AVEC response times during interrupt acknowledge cycles. The

monitor asserts BERR if response time is excessive.

DSACK and AVEC response times are measured in clock cycles. The maximum allowable response

time can be selected by setting the BMT field.

The monitor does not check DSACK response on the external bus unless the CPU initiates the bus cy-

cle. The BME bit in the SYPCR enables the internal bus monitor for internal to external bus cycles. If a

system contains external bus masters, an external bus monitor must be implemented and the internal

to external bus monitor option must be disabled.

3.2.4 Halt Monitor

The halt monitor responds to an assertion of HALT on the internal bus. A flag in the reset status register

(RSR) indicates that the last reset was caused by the halt monitor. The halt monitor reset can be inhib-

ited by the HME bit in the SYPCR.

SWP

SWT

Ratio

000

001

211

010

213

011

215

100

218

101

220

110

222

111

224

BMT

Bus Monitor Time-out Period

64 System Clocks

32 System Clocks

16 System Clocks

8 System Clocks

Freescale Semiconductor, Inc.

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