User Manual
Apollo3 Blue Datasheet
DS-A3-0p9p1 Page 531 of 909 2019 Ambiq Micro, Inc.
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12.2.2 CLKGEN Registers
12.2.2.1 CALXT Register
XT Oscillator Control
OFFSET: 0x00000000
INSTANCE 0 ADDRESS: 0x40004000
This is the XT Oscillator Calibration value. This value allows any derived XT clocks to be "calibrated". This
means that the original 32KHz version of XT will not be changed, but a 16KHz version (divided down
version) can be modified. This register value will add or subtract the number of cycles programmed in this
register across a 32 seconds interval. For example, if a value of 100 is programmed in this register, then
100 additional clock cycles will be added into a 16KHz clock period across a 32 second interval.
12.2.2.2 CALRC Register
RC Oscillator Control
OFFSET: 0x00000004
INSTANCE 0 ADDRESS: 0x40004004
This is the LFRC Calibration value. Similar to the XT calibration, it allows the derived LFRC clock to be
calibrated. The original 1024Hz clock source will not change, but a 512Hz version (divided down version)
can be modified. This register will add or subtract the number of cycles programmed in this register across
a 1024 seconds interval. For example, if a value of 200 is programmed in this register, then 200 additional
clocks will be added into the 512Hz derived clock across a 1024 seconds interval.
Table 760: CALXT Register
3
1
3
0
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
1
9
1
8
1
7
1
6
1
5
1
4
1
3
1
2
1
1
1
0
0
9
0
8
0
7
0
6
0
5
0
4
0
3
0
2
0
1
0
0
RSVD CALXT
Table 761: CALXT Register Bits
Bit Name Reset RW Description
31:11 RSVD 0x0 RO
RESERVED
10:0 CALXT 0x0 RW
XT Oscillator calibration value. This register will enable the hardware to
increase or decrease the number of cycles in a 16KHz clock derived from
the original 32KHz version. The most significant bit is the sign. A '1' is a
reduction, and a '0' is an addition. This calibration value will add or reduce
the number of cycles programmed here across a 32 second interval. The
maximum value that is effective is from -1024 to 1023.