User Manual

Apollo3 Blue Datasheet
DS-A3-0p9p1 Page 727 of 909 2019 Ambiq Micro, Inc.
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and the FIFO will be written with the final average value. When each active slot obtains a sample from the
ADC, it is added to the value in its accumulator.
If a slot is set to accumulate 128 samples per result then the accumulator could reach a maximum value of:
128*(2
14
-1) = 128*16383 = 2097024 = 2
21
- 128, hence the 21 bit accumulator.
Table 1066 shows the maximum possible accumulated values. Note that 64 sample accumulation
produces a result that is exactly correct or the 14.6 format results so it is copied unscaled in to the FIFO.
Furthermore, note that 128 sample accumulation can produce a result that is too large for the 14.6 format
since it may result in 7 bits of valid fractional data. All of the remaining sample accumulation settings must
have their results left shifted to produce the desired 14.6 format.
Finally, note that for the 128 sample accumulation case, the LSB of the accumulator is discarded when the
results are written to the FIFO.
Most importantly, note that for the 1 sample accumulation case, the 14-bit converter value is shifted left by
six to produce the 14.6 format to write into the FIFO.
18.2.7 Sixteen Entry Result FIFO
All results written to the FIFO have exactly the same format as shown in Table 1067. The properly scaled
accumulation results are written the lower half word in the aforementioned 14.6 format. Since each slot can
Table 1065: Per Slot Sample Accumulator
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
Accumulator
Table 1066: Accumulator Scaling
# Samples
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
128 14.6 0
64 X 14.6
32 X X 14.5
16 X X X 14.4
8 XXXX 14.3
4 XXXXX 14.2
2 XXXXXX 14.1
1 XXXXXXX 14