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System Integration Module (SIM)
MCF5253 Reference Manual, Rev. 1
9-18
Freescale Semiconductor
The SWT can be enabled or disabled using the SWE bit in the SYPCR. If enabled, the SWT requires the
execution of a software watchdog servicing sequence periodically. If this periodic servicing action does
not occur, the SWT times-out resulting in a SWT IRQ or hardware reset, as programmed by the SWRI bit
in the SYPCR.
If the SWT times out and the software watchdog transfer acknowledge enable (SWTA = SYPCR[2]) bit is
set in the system protection control register, the SWT IRQ will assert. If after another timeout and the SWT
IACK cycle has not occurred, the SWT TA signal will assert in an attempt to terminate the bus cycle and
allow IACK cycle to proceed. The setting of the SWTAVAL flag bit (SYPCR[1]) in the system protection
control register indicates that the SWT TA signal was asserted. The SWTA function when terminating a
locked bus is shown in
Figure 9-10. MCF5253 Unterminated Access Recovery
When the SWT times out and SWRI register bit is programmed for a software reset, an internal reset will
be asserted, and the SWTR register bit will be set in the RSR.
To prevent SWT from interrupting or resetting, users must service the SWSR register. The SWT service
sequence consists of the following steps:
1. Write $55 to SWSR
2. Write $AA to the SWSR
CODE ENABLES SWT INTERRUPT AND
1
. SWT TIMES-OUT DUE TO UN-TERMINATED BUS
2. UNABLE TO SERVICE SWT INTERRUPT DUE TO “HUNG” BUS
CYCLE. WAIT ANOTHER SWT TIMEOUT BEFORE setTING SWTA.
SWT TIMEOUT
SWT TIMEOUT
SWTAVAL
2
SWT TA
1
SWT IRQ
1
SWTA FUNCTIONALITY BY WRITING SYPCR
(
BIT 1 IN SYPCR)
SWT IACK CYCLE
CODE IN SWT INTERRUPT HANDLER POLLS THE
SWTAVAL BIT IN THE SYPCR TO DETERMINE
WHETHER OR NOT SWT TA WAS NEEDED.
IF SO, EXECUTE CODE TO IDENTIFY BAD ADDRESS.
3. HELD UNTIL ANOTHER
BUS CYCLE STARTS
PROBLEM:
NOTE: RECOMMEND THAT SWT IRQ
BE SET TO THE HIGHEST LEVEL IN THE SYSTEM.
1 SWT IRQ AND SWT TA ARE ACTIVE-LOW signals.
2 SWTAVAL IS SET TO ‘1’ IF SWT TA SIGNAL is ASSERTED.
Содержание MCF5253
Страница 1: ...Document Number MCF5253RM Rev 1 08 2008 MCF5253 Reference Manual...
Страница 26: ...MCF5253 Reference Manual Rev 1 xxvi Freescale Semiconductor...
Страница 32: ...MCF5253 Reference Manual Rev 1 xxxii Freescale Semiconductor...
Страница 46: ...MCF5253 Introduction MCF5253 Reference Manual Rev 1 1 14 Freescale Semiconductor...
Страница 62: ...Signal Description MCF5253 Reference Manual Rev 1 2 16 Freescale Semiconductor...
Страница 98: ...Instruction Cache MCF5253 Reference Manual Rev 1 5 10 Freescale Semiconductor...
Страница 104: ...Static RAM SRAM MCF5253 Reference Manual Rev 1 6 6 Freescale Semiconductor...
Страница 128: ...Synchronous DRAM Controller Module MCF5253 Reference Manual Rev 1 7 24 Freescale Semiconductor...
Страница 144: ...Bus Operation MCF5253 Reference Manual Rev 1 8 16 Freescale Semiconductor...
Страница 176: ...System Integration Module SIM MCF5253 Reference Manual Rev 1 9 32 Freescale Semiconductor...
Страница 198: ...Analog to Digital Converter ADC MCF5253 Reference Manual Rev 1 12 6 Freescale Semiconductor...
Страница 246: ...DMA Controller MCF5253 Reference Manual Rev 1 14 18 Freescale Semiconductor...
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