SN8P275X Series
8-bit micro-controller build-in 12-bit ADC
SONiX TECHNOLOGY CO., LTD
Page 139
Version 0.7
11.5 P4CON REGISTERS
The Port 4 is shared with ADC input function. Only one pin of port 4 can be configured as ADC input in the same time
by ADM register. The other pins of port 4 are digital I/O pins. Connect an analog signal to COMS digital input pin,
especially the analog signal level is about 1/2 VDD will cause extra current leakage. In the power down mode, the
above leakage current will be a big problem. Unfortunately, if users connect more than one analog input signal to port 4
will encounter above current leakage situation. P4CON is Port4 Configuration register. Write “1” into P4CON [7:0] will
configure related port 4 pin as pure analog input pin to avoid current leakage.
0AEH
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
P4CON
P4CON7 P4CON6 P4CON5 P4CON4 P4CON3 P4CON2 P4CON1 P4CON0
Read/Write R/W
R/W
R/W R/W R/W R/W R/W R/W
After
reset
0 0 0 0 0 0 0 0
Bit[4:0]
P4CON[7:0]:
P4.n configuration control bits.
0 = P4.n can be an analog input (ADC input) or digital I/O pins.
1 = P4.n is pure analog input, can’t be a digital I/O pin.
Note: When Port 4.n is general I/O port not ADC channel, P4CON.n must set to “0” or the Port 4.n digital
I/O signal would be isolated.
11.6 ADC CONVERTING TIME
12-bit ADC conversion time = 1/(ADC clock /4)*16 sec
8-bit ADC conversion time = 1/(ADC clock /4)*12 sec
Fcpu = 4MHz ( High clock, Fosc is 16MHz and Fcpu = Fosc/4)
ADLEN
ADCKS2 ADCKS1 ADCKS0
ADC Clock
ADC conversion time
0 0 0
Fcpu/16
1/(4MHz/16/4)*12
=
192
us
0
0
1
Fcpu/8
1/(4MHz/8/4)*12 = 96 us
0
1
0
Fcpu
1/(4MHz/4)*12 = 12 us
0 (8-bit)
0
1
1
Fcpu/2
1/(4MHz/2/4)*12 = 24 us
1 0 0
Fcpu/64
1/(4MHz/64/4)*12
=
768
us
1 0 1
Fcpu/32
1/(4MHz/32/4)*12
=
384
us
1
1
0
Fcpu/4
1/(4MHz/4/4)*12 = 48 us
0 (8-bit)
1 1 1
Reserved Reserved
0 0 0
Fcpu/16
1/(4MHz/16/4)*16
=
256
us
0
0
1
Fcpu/8
1/(4MHz/8/4)*16 = 128 us
0
1
0
Fcpu
1/(4MHz/4)*16 = 16 us
1 (12-bit)
0
1
1
Fcpu/2
1/(4MHz/2/4)*16 = 32 us
1 0 0
Fcpu/64
1/(4MHz/64/4)*16
=
1024
us
1 0 1
Fcpu/32
1/(4MHz/32/4)*16
=
512
us
1
1
0
Fcpu/4
1/(4MHz/4/4)*16 = 64 us
1 (12-bit)
1 1 1
Reserved Reserved