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Rev. 1.00
108
October 26, 2018
Rev. 1.00
109
October 26, 2018
BS86DH12C
High Voltage Touch A/D Flash MCU with HVIO
BS86DH12C
High Voltage Touch A/D Flash MCU with HVIO
that can be selected. As the recommended range of permissible A/D clock period, t
ADCK
, is from 0.5μs
to 10μs, care must be taken for system clock frequencies. For example, if the system clock operates
at a frequency of 8MHz, the SACKS2~SACKS0 bits should not be set to 000, 001 or 111. Doing
so will give A/D clock periods that are less than the minimum A/D clock period or greater than the
maximum A/D clock period which may result in inaccurate A/D conversion values. Refer to the
following table for examples, where values marked with an asterisk * show where, special care must
be taken, as the values may be beyond the specified A/D Clock Period range.
f
SYS
A/D Clock Period (t
ADCK
)
SACKS[2:0]
= 000
(f
SYS
)
SACKS[2:0]
= 001
(f
SYS
/2)
SACKS[2:0]
= 010
(f
SYS
/4)
SACKS[2:0]
= 011
(f
SYS
/8)
SACKS[2:0]
= 100
(f
SYS
/16)
SACKS[2:0]
= 101
(f
SYS
/32)
SACKS[2:0]
= 110
(f
SYS
/64)
SACKS[2:0]
= 111
(f
SYS
/128)
1MHz
1μs
2μs
4μs
8μs
16μs *
32μs *
64μs *
128μs *
2MHz
500ns
1μs
2μs
4μs
8μs
16μs *
32μs *
64μs *
4MHz
250ns *
500ns
1μs
2μs
4μs
8μs
16μs *
32μs *
8MHz
125ns *
250ns *
500ns
1μs
2μs
4μs
8μs
16μs *
12MHz
83ns*
167ns*
333ns*
667ns
1.33μs
2.67μs
5.33μs
10.67μs*
16MHz
62.5ns*
125ns*
250ns*
500ns
1μs
2μs
4μs
8μs
A/D Clock Period Examples
Controlling the power on/off function of the A/D converter circuitry is implemented using the
ADCEN bit in the SADC0 register. This bit must be set high to power on the A/D converter. When
the ADCEN bit is set high to power on the A/D converter internal circuitry, a certain delay, as
indicated in the timing diagram, must be allowed before an A/D conversion is initiated. Even if no
pins are selected for use as A/D inputs by configuring the relevant pin-shared control bits, if the
ADCEN bit is high, then some power will still be consumed. In power conscious applications it is
therefore recommended that the ADCEN is set low to reduce power consumption when the A/D
converter function is not being used.
Conversion Rate and Timing Diagram
A complete A/D conversion contains two parts, data sampling and data conversion. The data
sampling which is defined as t
ADS
takes 4 A/D clock cycles and the data conversion takes 12 A/D
clock cycles. Therefore a total of 16 A/D clock cycles for an analog signal A/D conversion which is
defined as t
ADC
are necessary.
Maximum single A/D conversion rate=A/D clock period / 16
The accompanying diagram shows graphically the various stages involved in an external channel
input signal analog to digital conversion process and its associated timing. After an A/D conversion
process has been initiated by the application program, the microcontroller internal hardware will
begin to carry out the conversion, during which time the program can continue with other functions.
The time taken for the A/D conversion is 16 t
ADCK
clock cycles where t
ADCK
is equal to the A/D clock
period.