SN8P2711A
8-Bit Micro-Controller
SONiX TECHNOLOGY CO., LTD
Page 108
Version 0.1
9.6 VREFH
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 CMOS 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.
Note:
a. ADC resolution is 8-bit if use internal 4V/3V/2V reference voltage.
b. ADC resolution is 12-bit if use Internal VDD reference voltage or use external reference voltage.
0AFH
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
VREFH
EVHENB
- - - - -
VHS1
VHS0
Read/Write
R/W
- - - - -
R/W
R/W
After
reset
0 - - - - - 0 0
Bit[1:0]
VHS[1:0]:
ADC internal reference high voltage select bits.
VHS1
VHS0 Internal VREFH Voltage
1 1
VDD
1 0
4.0V
0 1
3.0V
0 0
2.0V
Note: If internal VREFH level selected by VHS[1:0] is higher than VDD, the internal VREFH is VDD. For
instance, VHS[1:0] is 10 (internal VREFH = 4.0V) and VDD is 3.0V, the actual internal VREFH is equal to
VDD (3.0V).
Bit[7]
EVHENB:
ADC internal reference high voltage control bit.
0 = Enable ADC internal VREFH function, P4.0/AIN0/VREFH pin is P4.0/AIN0 pin.
1 = Disable ADC internal VREFH function, P4.0/AIN0/VREFH pin is external VREFH input pin.
Note: If EVHENB = 1, P4.0/AIN0 pin is external VREFH input pin and P4.0 I/O and AIN0 functions are
isolated.
