C8051T603-GS(2007) 查看數據表（PDF） - Silicon Laboratories
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C8051T603-GS Datasheet PDF : 168 Pages
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C8051T600/1/2/3/4/5
6. Voltage Reference Options
The voltage reference MUX is configurable to use an externally connected voltage reference, the unregu-
lated power supply voltage (VDD), or the regulated 1.8 V internal supply (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 VDD as the reference source, REFSL should be set to ‘1’. To override this selec-
tion, and use the internal regulator as the reference source, the REGOVR bit can be set to ‘1’. See
Figure 6.1 for REF0CN register details. The electrical specifications for the voltage reference circuit 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 “13. Port Input/Output” on page 97 for complete
Port I/O configuration details. The external reference voltage must be within the range 0 ≤ VREF ≤ VDD.
On C8051T600/2 devices, the temperature sensor connects to the highest order input of the ADC0 positive
input multiplexer (see Section “5.1. Analog Multiplexer” on page 32 for details). The TEMPE bit in regis-
ter 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 meaningless
data.
REF0CN
VDD
R1
External
Voltage
Reference
Circuit
GND
EN Temp Sensor
VREF
REGOVR
0
0
VDD 1
Internal
Regulator
1
To Analog Mux
VREF
(to ADC)
Figure 6.1. Voltage Reference Functional Block Diagram
Rev. 0.5
45
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