mc68332acpv25b1 Freescale Semiconductor, Inc, mc68332acpv25b1 Datasheet - Page 21

• Manufacturer Part Number: mc68332acpv25b1
• Description: Technical Summary 32-bit Modular Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

3.2.3 Bus Monitor
3.2.4 Halt Monitor
3.2.5 Spurious Interrupt Monitor
3.2.6 Software Watchdog
SWSR —Software Service Register
MC68332
MC68332TS/D
RESET:
15
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.
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.
The spurious interrupt monitor issues BERR if no interrupt arbitration occurs during an interrupt-ac-
knowledge cycle.
The software watchdog is controlled by SWE in the SYPCR. Once enabled, the watchdog requires that
a service sequence be written to SWSR on a periodic basis. If servicing does not take place, the watch-
dog times out and issues a reset. This register can be written at any time, but returns zeros when read.
Register shown with read value
Both writes must occur before time-out in the order listed, but any number of instructions can be exe-
cuted between the two writes.
The watchdog clock rate is affected by SWP and SWT in SYPCR. When SWT[1:0] are modified, a
watchdog service sequence must be performed before the new time-out period takes effect.
The reset value of SWP is affected by the state of the MODCLK pin on the rising edge of reset, as shown
in the following table.
Perform a software watchdog service sequence as follows:
a. Write $55 to SWSR.
b. Write $AA to SWSR.
NOT USED
Freescale Semiconductor, Inc.
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MODCLK
0
1
8
7
0
0
SWP
1
0
6
0
0
5
0
0
4
0
0
3
0
0
2
0
0
MOTOROLA
$YFFA27
1
0
0
0
0
0
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