Si1010/1/2/3/4/5
5.1. Output Code Formatting
The registers ADC0H and ADC0L contain the high and low bytes of the output conversion code from the
ADC at the completion of each conversion. Data can be right-justified or left-justified, depending on the
setting of the AD0SJST[2:0]. When the repeat count is set to 1, conversion codes are represented as 10-
bit unsigned integers. Inputs are measured from 0 to VREF x 1023/1024. Example codes are shown below
for both right-justified and left-justified data. Unused bits in the ADC0H and ADC0L registers are set to 0.
Input Voltage
VREF x 1023/1024
VREF x 512/1024
VREF x 256/1024
0
Right-Justified ADC0H:ADC0L
(AD0SJST = 000)
0x03FF
0x0200
0x0100
0x0000
Left-Justified ADC0H:ADC0L
(AD0SJST = 100)
0xFFC0
0x8000
0x4000
0x0000
When the repeat count is greater than 1, the output conversion code represents the accumulated result of
the conversions performed and is updated after the last conversion in the series is finished. Sets of 4, 8,
16, 32, or 64 consecutive samples can be accumulated and represented in unsigned integer format. The
repeat count can be selected using the AD0RPT bits in the ADC0AC register. When a repeat count higher
than 1, the ADC output must be right-justified (AD0SJST = 0xx); unused bits in the ADC0H and ADC0L
registers are set to 0. The example below shows the right-justified result for various input voltages and
repeat counts. Notice that accumulating 2
n
samples is equivalent to left-shifting by
n
bit positions when all
samples returned from the ADC have the same value.
Input Voltage
V
REF
x 1023/1024
V
REF
x 512/1024
V
REF
x 511/1024
0
Repeat Count = 4
0x0FFC
0x0800
0x07FC
0x0000
Repeat Count = 16
0x3FF0
0x2000
0x1FF0
0x0000
Repeat Count = 64
0xFFC0
0x8000
0x7FC0
0x0000
The AD0SJST bits can be used to format the contents of the 16-bit accumulator. The accumulated result
can be shifted right by 1, 2, or 3 bit positions. Based on the principles of oversampling and averaging, the
effective ADC resolution increases by 1 bit each time the oversampling rate is increased by a factor of 4.
The example below shows how to increase the effective ADC resolution by 1, 2, and 3 bits to obtain an
effective ADC resolution of 11-bit, 12-bit, or 13-bit respectively without CPU intervention.
Input Voltage
Repeat Count = 4
Shift Right = 1
11-Bit Result
0x07F7
0x0400
0x03FE
0x0000
Repeat Count = 16
Shift Right = 2
12-Bit Result
0x0FFC
0x0800
0x04FC
0x0000
Repeat Count = 64
Shift Right = 3
13-Bit Result
0x1FF8
0x1000
0x0FF8
0x0000
V
REF
x 1023/1024
V
REF
x 512/1024
V
REF
x 511/1024
0
78
Rev. 1.0
SILABS [ SILICON LABORATORIES ]
