Refresh Control Unit
6-4
Bit 11: Test Mode (TEST)—This bit is reserved for an internal test mode. Setting this bit
activates a special test mode that generates early WDT timeouts. This bit is 0 after processor
reset.
Bits 10–8: Reserved
Bits 7–0: WDT Timeout Count (COUNT)—This field determines the duration of the
watchdog timer timeout interval. The duration is determined by using the value from the
column titled Exponent in Table 6-1 in the following equation.
Duration = 2
Exponent
/ Frequency
Where Duration is the timeout period in seconds, Exponent is the value from Table 6-2,
and Frequency is the processor frequency in Hz. For example, the following calculation
determines the WDT timeout period for a 40-MHz processor with the COUNT field set to 20h.
Duration
= (2
24
cycles) / (40,000,000 Hz)
= (16,777,216 cycles) / (40,000,000 cycles/second)
= .4194 seconds
Setting more than one bit in the COUNT field results in the shorter timeout value. This field
is 80h after reset.
Table 6-1
Watchdog Timer COUNT Settings
Table 6-2
Watchdog Timer Duration
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Exponent
0
0
0
0
0
0
0
0
N/A
X
X
X
X
X
X
X
1
10
X
X
X
X
X
X
1
0
20
X
X
X
X
X
1
0
0
21
X
X
X
X
1
0
0
0
22
X
X
X
1
0
0
0
0
23
X
X
1
0
0
0
0
0
24
X
1
0
0
0
0
0
0
25
1
0
0
0
0
0
0
0
26
Exponent
20 MHz
25 MHz
33 MHz
40 MHz
10
51
µ
s
40
µ
s
30
µ
s
25
µ
s
20
52 ms
41 ms
31 ms
26 ms
21
104 ms
83 ms
62 ms
52 ms
22
209 ms
167 ms
125 ms
104 ms
23
419 ms
335 ms
251 ms
209 ms
24
838 ms
671 ms
503 ms
419 ms
25
1.67 s
1.34 s
1.00 s
838 ms
26
3.35 s
2.68 s
2.01 s
1.67 s
Summary of Contents for Am186 ES
Page 1: ...Am186 ES and Am188 ES User s Manual...
Page 4: ...iv...
Page 12: ...Table of Contents xii...
Page 22: ...Features and Performance 1 8...
Page 60: ...System Overview 3 28...
Page 84: ...Chip Select Unit 5 14...
Page 132: ...Timer Control Unit 8 8...
Page 166: ...Programmable I O Pins 11 6...
Page 184: ...Register Summary A 18...