RK3288 Hardware Design Guide
12 SarADC & Key
12.1 Schematic
RK3288 adapt SARADC ADC_IN1 as input key-value sampling port, RECOVER mode is
available ( don't need to update LOADER) as shown in Fig 12-1.Under the premise of system
has a hardware, system will start up after pressing SW1500, and ADC_IN1 will keep OV
level(maximum will not exceed 100mV), RK3288 will enter Rockusb burning mode. If USB
device is detected by PC, upon release of button, ADC_IN1 will recover high level (1.8V), then
firmware updating is available.
On RK3288, SARADC sampling range is 0-1.8V, sampling accuracy is 10bit. Input
key-value can be adjusted by changing key numbers in key array and divider resistance ratio,
we can meet customer product demand by realizing multi-key inputs. Two key-values voltage
must be more than 250mV in design.
Fig 12-1
Tips：
Recover mode entering method can't be changed by customer;
Even if the keys are not necessary in design, ADC_IN1 pull-up resistor R1500 must be
reserved.
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