C8051F80X_14 Datasheet, PDF (60/251 Pages) Silicon Laboratories – Mixed Signal ISP Flash MCU Family

C8051F80x-83x
10. Voltage and Ground Reference Options
The voltage reference MUX is configurable to use an externally connected voltage reference, the on-chip
voltage reference, or one of two power supply voltages (see Figure 10.1). The ground reference MUX
allows the ground reference for ADC0 to be selected between the ground pin (GND) or a port pin dedi-
cated to analog ground (P0.1/AGND).
The voltage and ground reference options are configured using the REF0CN SFR described on page 62.
Electrical specifications are can be found in the Electrical Specifications Chapter.
Important Note About the V_REF and AGND Inputs: Port pins are used as the external V_REF and AGND
inputs. When using an external voltage reference, P0.0/VREF should be configured as an analog input and
skipped by the Digital Crossbar. When using AGND as the ground reference to ADC0, P0.1/AGND should
be configured as an analog input and skipped by the Digital Crossbar. Refer to Section “23. Port Input/Out-
put” on page 138 for complete Port I/O configuration details. The external reference voltage must be within
the range 0  V_REF  V_DD and the external ground reference must be at the same DC voltage potential as
GND.
REF0CN
VDD
R1
External
Voltage
Reference
Circuit
P0.0/VREF
V_DD
GND
+
4.7F
0.1F
GND
Recommended
Bypass Capacitors
P0.1/AGND
EN _{Bias Generator}
IOSCEN
EN _{Temp Sensor}
To ADC, Internal
Oscillator,
Reference,
TempSensor
To Analog Mux
00
01
Internal 1.8V
10
Regulated Digital Supply
11
Internal 1.65V
High Speed Reference
0
1
REFGND
Figure 10.1. Voltage Reference Functional Block Diagram
60
Rev. 1.0