mcf5282 Freescale Semiconductor, Inc, mcf5282 Datasheet - Page 159

• Manufacturer Part Number: mcf5282
• Manufacturer: Freescale Semiconductor, Inc

8.4.5
The software watchdog service sequence must be performed using the CWSR as a data register to prevent
a CWT time-out. The service sequence requires two writes to this data register: first a write of 0x55
followed by a write of 0xAA. Both writes must be performed in this order prior to the CWT time-out, but
any number of instructions or accesses to the CWSR can be executed between the two writes. If the CWT
has already timed out, writing to this register has no effect in negating the CWT interrupt.
illustrates the CWSR. At system reset, the contents of CWSR are uninitialized.
8.5
The internal bus arbitration is performed by the on-chip bus arbiter, which containing the arbitration logic
that controls which of up to four MBus masters (M0–M3 in
The function of the arbitration logic is described in this section.
Freescale Semiconductor
5–3
2
1
0
Internal Bus Arbitration
CWTAVAL Core watchdog transfer acknowledge valid.
CWT[2:0] Core watchdog timing delay. These bits select the timeout period for the CWT. At system reset, the
Core Watchdog Service Register (CWSR)
CWTIF
CWTA
Address
Reset
CWT field is cleared signaling the minimum time-out period but the watchdog is disabled
(CWCR[CWE] = 0).
Core watchdog transfer acknowledge enable.
0 CWTA Transfer acknowledge disabled.
1 CWTA Transfer Acknowledge enabled. After one CWT time-out period of the unacknowledged
0 CWTA Transfer Acknowledge has not occurred.
1 CWTA Transfer Acknowledge has occurred. Write a 1 to clear this flag bit.
Core watchdog timer interrupt flag.
0 CWT interrupt has not occurred
1 CWT interrupt has occurred. Write a 1 to clear the interrupt request.
Field
R/W
assertion of the CWT interrupt, the transfer acknowledge asserts, which allows CWT to terminate
a bus cycle and allow the interrupt acknowledge to occur.
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3
Figure 8-5. Core Watchdog Service Register (CWSR)
CWT
000
001
010
011
7
Table 8-5. CWCR Field Description (continued)
2
2
2
CWT Time-Out Period
2
11
13
15
9
Bus clock frequency
Bus clock frequency
Bus clock frequency
Bus clock frequency
IPSBAR + 0x013
Uninitialized
CWSR[7:0]
R/W
Figure
CWT
100
101
110
111
8-6) has access to the external buses.
2
2
2
2
CWT Time-Out Period
19
23
27
31
Bus clock frequency
Bus clock frequency
Bus clock frequency
Bus clock frequency
System Control Module (SCM)
0
Figure 8-5
8-7