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CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
10-Bit SAR ADC Controller
35.1.6
‘Ready’ Bit, ‘Ongoing’ Bit and
Interrupt
In SADC_CR0, two status bits are used to reflect ADC sta-
tus. The first is the ‘Ready’ bit, which is set when the ADC
data register receives new data. It can only be cleared when
the SADC_DH register is read, unless other new data
arrives. The second status bit is the ‘Ongoing’ bit, which is
the inverse of IDLE.
The ADC interrupt occurs when there is new data.
35.1.7
Converted Data Format and Read
Sequence
The converted data is stored in two registers: SADC_DH
(0,6Ah) and SADC_DL (0,6Bh). Both are 8-bit registers. By
default the converted 10-bit data is right-justified, so the
highest 6 bits in SADC_DH are always ‘0’. {ADC_DH[1:0],
ADC_DL[7:0]} form the 10-bit ADC data. The 10-bit data can
be left-justified by setting SADC_CR3 bit 7 as 1, and then
the highest 6 bits in SADC_DL are always 0s.
{SADC_DH[7:0], SADC_DL[1:0]} form the 10-bit ADC data.
Because there are always two reads to read DH and DL, an
internal lock mechanism is required to avoid data conflict. In
right-justified mode, SADC_DL should be read first, then
SADC_DH follows. In left-justified mode, SADC_DH should
be read first, then SADC_DL follows. The register containing
the most useful bits should be read first.
35.2
Application Description
35.2.1
ADC Sample Rate and Clock
Selection
The ADC sample rates are maximum< 142 ksps and mini-
mum > 26.7 ksps, based on
35.2.2
Voltage Doubler Enable
Enable the voltage doubler when Vcc is less than 3.0 V.
Note that this voltage doubler enable is not gated off by ADC
enable. To achieve a low power state, turn it OFF.
35.2.3
Reference Selection
Table 35-3. ADC Sample Rate and Clock Selection
SYSCLK
(IMO)
Fastest
Slowest
Clock
Setting
Actual SPS
Clock
Setting
Actual SPS
24 MHz
SYSCLK/12
142.8 ksps
SYSCLK/64
26.7 ksps
Table 35-4. SAR ADC Reference Selection
a
a. “X” = Don’t Care/
REFSEL
b
b. REFSEL is bit 7 of SADC_CR2
BUFEN
c
c. BUFEN is bit 6 of SADC_CR2
EXTREF
d
d. EXTREF is bit 7 of SADC_CR3
ADC Reference Selection
0
X
X
Selects VDD
1
0
0
Selects UNBUFFERED Internally
(REFHI) generated Reference Voltage
supply
2.4 V
VREF
VDD – 0.3 V
1
0
1
Selects UNBUFFERED Externally
forced Reference Voltage supply (input
on P2.5)
2.4 V
VREF
VDD – 0.3 V
1
1
0
Selects BUFFERED Internally (REFHI)
generated Reference Voltage supply
2.4 V
VREF
VDD – 0.3 V
(Through ADC Internal Reference
Buffer)
1
1
1
Selects BUFFERED Externally forced
Reference Voltage supply (input on
P2.5)
2.4 V
VREF
VDD – 0.3 V
(Through ADC Internal Reference
Buffer)
Summary of Contents for CY8C28 series
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