C8051F310 datasheet(67/228 Pages) SILABS

67 / 228 page

Rev. 1.7

C8051F310/1/2/3/4/5/6/7

Voltage Reference (C8051F310/1/2/3/6 only)

The voltage reference MUX on C8051F310/1/2/3/6 devices is configurable to use an externally connected

voltage reference, or the power supply voltage (see Figure 6.1). The REFSL bit in the Reference Control

VDD as the reference source, REFSL should be set to ‘1’.

The BIASE bit enables the internal voltage bias generator, which is used by the ADC, Temperature Sensor,

and Internal Oscillator. This bit is forced to logic 1 when any of the aforementioned peripherals is enabled.

The bias generator may be enabled manually by writing a ‘1’ to the BIASE bit in register REF0CN; see

SFR Definition 6.1 for REF0CN register details. The electrical specifications for the voltage reference cir-

cuit are given in Table 6.1.

Important Note About the VREF Input: Port pin P0.0 is used as the external VREF input. When using an

external voltage reference, P0.0 should be configured as analog input and skipped by the Digital Crossbar.

To configure P0.0 as analog input, set to ‘0’ Bit0 in register P0MDIN. To configure the Crossbar to skip

P0.0, set to ‘1’ Bit0 in register P0SKIP. Refer to Section “13. Port Input/Output” on page 129 for com-

plete Port I/O configuration details.

The temperature sensor connects to the highest order input of the ADC0 positive input multiplexer (see

Section “5.1. Analog Multiplexer” on page 51 for details). The TEMPE bit in register REF0CN

enables/disables the temperature sensor. While disabled, the temperature sensor defaults to a high imped-

ance state and any ADC0 measurements performed on the sensor result in meaningless data.

Figure 6.1. Voltage Reference Functional Block Diagram

Internal

VREF

(to ADC)

To Analog Mux

VDD

VREF

VDD

External

Voltage

Reference

Circuit

GND

REF0CN

Temp Sensor

Bias Generator

To ADC, Internal

Oscillator

IOSCEN

C8051F310 Datasheet(PDF) 67 Page - Silicon Laboratories