Core Timer
Registers
MC68HC(7)05H12
—
Rev. 1.0
General Release Specification
MOTOROLA
Core Timer
101
L
G
R
8.3.2 Computer Operating Properly (COP) Watchdog Reset
The COP watchdog timer function is implemented on this device by
using the output of the RTI circuit and further dividing it by eight. The
minimum COP reset rates are listed in
Table 8-2
. If the COP circuit times
out, an internal reset is generated and the normal reset vector is fetched.
Preventing a COP time-out is done by writing a ‘0’ to bit 0 of address
$3FF0. When the COP is cleared, only the final divide by eight stage
(output of the RTI) is cleared.
8.3.3 Core Timer Counter Register (CTCR)
The timer counter register is a read-only register which contains the
current value of the 8-bit ripple counter at the beginning of the timer
chain. This counter is clocked at f
op
divided by 4 and can be used for
various functions including a software input capture. Extended time
periods can be attained using the TOF function to increment a temporary
RAM storage location thereby simulating a 16-bit (or more) counter.
01
65.536ms
32.768ms
16.384ms
13.333ms
2
15
/f
op
2
16
/f
op
2
17
/f
op
10
131.072ms
65.536ms
32.768ms
26.667ms
11
262.144ms
131.072ms
65.536ms
53.333ms
Table 8-1. RTI Rates
RTI Rates at Bus Frequency f
OP
specified:
RT1:RT0
500 kHz
1.000 MHz
2.000 MHz
2.4576 MHz
RATIO
Table 8-2. Minimum COP Reset Times
Minimum COP Reset Bus Frequency at f
OP
specified:
RT1:RT0
500 kHz
1.000 MHz
2.000 MHz
2.4576 MHz
RATIO
00
229.376ms
114.689ms
57.344ms
46.666ms
7*2
14
/f
op
7*2
15
/f
op
7*2
16
/f
op
7*2
17
/f
op
01
458.752ms
229.376ms
114.689ms
93.333ms
10
917.504ms
458.752ms
229.376ms
186.666ms
11
1835.000ms
917.504ms
458.752ms
373.333ms