Motorola MC68VZ328 - Manual (Page 224)

11-14 MC68VZ328 User’s Manual
Programming Model
11.2.9 Stopwatch Minutes Register
The stopwatch minutes (STPWCH) register contains the current stopwatch countdown value. The
stopwatch counter is decremented by the minute (MIN) output from the TOD clock. The average tolerance
of the count is 0.5 minutes. The settings for the STPWCH register are described in Table 11-11.
NOTE:
For improved accuracy, enable the stopwatch by polling the MIN bit of the
RTCISR register or by polling the minute interrupt service routine.
STPWCH Stopwatch Minutes Register 0x(FF)FFFB12
ALM
Bit 2 Alarm Interrupt Enable—This bit enables the alarm
interrupt. 0 = Alarm interrupt is disabled.
1 = Alarm interrupt is enabled.
MIN
Bit 1 Minute Interrupt Enable—This bit enables the MIN
interrupt at the rate of one interrupt per minute. 0 = 1-minute interrupt is disabled.
1 = 1-minute interrupt is enabled.
SW
Bit 0 Stopwatch Interrupt Enable—This bit enables the
stopwatch interrupt.
Note: The stopwatch counts down and remains at
decimal -1 until it is reprogrammed. If this bit is enabled
with -1 (decimal) in the STPWCH register, an interrupt
will be posted on the next minute tick.
0 = 1-minute interrupt is disabled.
1 = 1-minute interrupt is enabled.
BIT
15
14 13 12 11 10 9 8 7 6 5 4 3 2 1
BIT
0
CNT
TYPE rw rw rw rw rw rw
RESET
0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1
0x003F
Table 11-11. Stopwatch Minutes Register Description
Name Description Setting
Reserved
Bits 15–6 Reserved These bits are reserved and should be set to 0.
CNT
Bits 5–0 Stopwatch Count—This field contains
the stopwatch countdown value. The highest possible value is 62 minutes. The
countdown will not be activated again until a non-
zero value, which is less than 63 minutes, is written
to this register.
Table 11-10. RTC Interrupt Enable Register Description (Continued)
Name Description Setting