UG-1262
Rev. B | Page 301 of 312
Bits
Bit
Name
Settings Description
Reset Access
[5:0] CNTMOD60
Modulo 60 Value of the WUT Count. CNTMOD60 is the modulo 60 value of the
prescaled WUT count in CNT1 and CNT0. CNTMOD60 counts from 0 to 59 and
then rolls over to 0 again. It advances and is trimmed in tandem with the main
WUT count in CNT1, CNT0, and CNT2. CNTMOD60 is zeroed during a normal roll
over from a value of 59 when advancing at a prescaled time unit, when the CPU
writes a new pair of values to the CNT1 and CNT0 registers to redefine the
elapsed time count while the WUT is enabled and this posted twin write is
executed, when the CPU enables the WUT from a disabled state using the
CNTEN bit of CR0, or while the WUT is enabled via CNTEN. The degree of
prescaling in the WUT is changed by PRESCALE2EXP in CR1.
0x0 R
COUNT 2 REGISTER
Address: 0x40001440, Reset: 0x0000, Name: CNT2
CNT2 contains the fractional part of the WUT count, where the count is denominated in prescaled time units and is given by CNT1,
CNT0, and CNT2. The overall resolution of the real-time count, including the fractional bits in CNT2, is one 32 kHz clock period.
CNT2 makes available to the CPU a read only view of the internal sequence count in the WUT prescaler as it steps its way (in units of
one 32 kHz period) from all zeros to all ones across the number of prescale sequence bits given by the PRESCALE2EXP field of CR1. By
completely traversing such a sequence, the prescaler effectively advances the main nonfractional part of the WUT count in CNT1 and
CNT0 by one prescaled time unit. The prescale sequence count thus equates to the fractional part of the main WUT count.
Table 394. Bit Descriptions for CNT2
Bits Bit
Name Settings Description
Reset Access
15 Reserved
Reserved.
0x0 R
[14:0] VALUE
Fractional Bits of the WUT Real-Time Count. CNT2 contains the fractional part of the
WUT count, where the count is denominated in prescaled time units and is given by
CNT1, CNT0, and CNT2. The overall resolution of the real-time count, including the
fractional bits in CNT2, is therefore one 32 kHz clock period. CNT2 is zeroed during the
CPU writes a new pair of values to the CNT1 and CNT0 registers to redefine the elapsed
time units count while the WUT is enabled and this posted twin write is executed, when
the CPU enables the WUT from a disabled state using the CNTEN bit of CR0, or when the
WUT is enabled. The degree of prescaling in the WUT is changed by PRESCALE2EXP in CR1.
0x0 R
ALARM 2 REGISTER
Address: 0x40001444, Reset: 0x0000, Name: ALM2
ALM2 specifies the fractional nonprescaled bits of the WUT alarm target time value, down to an individual 32 kHz clock cycle, where the
overall alarm is defined as ALM1, ALM0, and ALM2.
The number of valid bits that can legitimately have values of one optionally written to them in ALM2 equals the number of prescale bits
specified by the PRESCALE2EXP bit field of the CR1 MMR. If a bit position in ALM2 is set to one, such that this is incompatible with
PRESCALE2EXP, the whole value of ALM2 is treated by the WUT as if it were zero.
Any write to ALM2 pends until corresponding writes to ALM0 and ALM1 are carried out by the CPU, so that the combined 47-bit alarm
redefinition can be executed as a single transaction. ALM0, ALM1, and ALM2 can be written in any order, but coordinated, triple writes
must be carried out by the CPU to have any effect on the WUT alarm. ALM2 can be written to regardless of whether ALMEN or CNTEN
is active in the CR0 register.
In contrast, on RTC1, full support for the fractional alarm time is present, such that an alarm can be specified down to an individual
32 kHz clock cycle using ALM2.
Table 395. Bit Descriptions for ALM2
Bits Bit
Name
Settings
Description
Reset Access
15 Reserved
Reserved.
0x0 R
[14:0] VALUE
Fractional Nonprescaled Bits of the WUT Alarm Target Time. Note that any value written
to ALM2 must be in keeping with the number of prescale bits specified by the
PRESCALE2EXP field of the CR1 MMR. If a value in ALM2 cannot be reached by the
degree of prescaling configured by PRESCALE2EXP, the whole value of ALM2 is treated
as if it were zero.
0x0 R/W