ISD94100 Series Technical Reference Manual
Sep 9, 2019
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Rev1.09
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HIRC Trim Control Register (SYS_IRCTCTL)
Register
Offset
R/W Description
Reset Value
SYS_IRCTCTL
0xF0
R/W HIRC Trim Control Register
0x0000_0000
31
30
29
28
27
26
25
24
Reserved
23
22
21
20
19
18
17
16
Reserved
15
14
13
12
11
10
9
8
Reserved
REFCKSEL
Reserved
CESTOPEN
7
6
5
4
3
2
1
0
RETRYCNT
LOOPSEL
Reserved
FREQSEL
Bits
Description
[31:11]
Reserved
Reserved. Any values read should be ignored. When writing to this field always write with
reset value.
[10]
REFCKSEL
Reference Clock Selection
0 = HIRC trim reference clock is from LXT (32.768 kHz).
1 = HIRC trim reference clock is from USB SOF (Start-Of-Frame) packet.
[9]
Reserved
Reserved. Any values read should be ignored. When writing to this field always write with
reset value.
[8]
CESTOPEN
Clock Error Stop Enable Bit
0 = The trim operation is keep going if clock is inaccuracy.
1 = The trim operation is stopped if clock is inaccuracy.
[7:6]
RETRYCNT
Trim Value Update Limitation Count
This field defines that how many times the auto trim circuit will try to update the HIRC trim
value before the frequency of HIRC locked.
Once the HIRC locked, the internal trim value update counter will be reset.
If the trim value update counter reached this limitation value and frequency of HIRC still
doesn’t lock, the auto trim operation will be disabled and FREQSEL will be cleared to 00.
00 = Trim retry count limitation is 64 loops.
01 = Trim retry count limitation is 128 loops.
10 = Trim retry count limitation is 256 loops.
11 = Trim retry count limitation is 512 loops.
[5:4]
LOOPSEL
Trim Calculation Loop Selection
This field defines that trim value calculation is based on how many reference clocks.
00 = Trim value calculation is based on average difference in 4 clocks of reference clock.
01 = Trim value calculation is based on average difference in 8 clocks of reference clock.
10 = Trim value calculation is based on average difference in 16 clocks of reference clock.
11 = Trim value calculation is based on average difference in 32 clocks of reference clock.
Note:
For example, if LOOPSEL is set as 00, auto trim circuit will calculate trim value based
