C8051F300 Datasheet, PDF (47/176 Pages) List of Unclassifed Manufacturers – Mixed Signal ISP Flash MCU Family

C8051F300/1/2/3/4/5
6. Voltage Reference (C8051F300/2)
The voltage reference MUX on C8051F300/2 devices is configurable to use an externally connected volt-
age reference or the power supply voltage, V_DD (see Figure 6.1). The REFSL bit in the Reference Control
register (REF0CN) selects the reference source. For an external source, REFSL should be set to ‘0’; For
V_DD 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 ‘1’ Bit0 in register P0MDIN. To configure the Crossbar to skip
P0.0, set to ‘1’ Bit0 in register XBR0. Refer to Section “12. Port Input/Output” on page 101 for complete
Port I/O configuration details. The external reference voltage must be within the range 0 ≤ VREF ≤ V_DD.
On C8051F300/2 devices, the temperature sensor connects to the highest order input of the ADC0 positive
input multiplexer (see Section “5.1. Analog Multiplexer and PGA” on page 34 for details). The TEMPE
bit in register REF0CN enables/disables the temperature sensor. While disabled, the temperature sensor
defaults to a high impedance state and any ADC0 measurements performed on the sensor result in mean-
ingless data.
REF0CN
VDD
R1
External
Voltage
Reference
Circuit
GND
VREF
IOSCEN
EN _{Bias Generator}
EN _{Temp Sensor}
0
VDD 1
To ADC, Internal
Oscillator,
Temperature Sensor
To Analog Mux
Internal
VREF
(to ADC)
Figure 6.1. Voltage Reference Functional Block Diagram
Rev. 2.8
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