C8051F2XX Datasheet, PDF (50/146 Pages) Silicon Laboratories – Mixed Signal 8 kB ISP Flash MCU Family

C8051F2xx
7. Voltage Reference (C8051F206/220/221/226)
The voltage reference circuit selects between an externally connected reference and the power supply
voltage (V_DD). (See Figure 7.1).
An external reference can be connected to the VREF pin and selected by setting the REF0CN special
function register per Figure 7.1. The external reference supply must be between V_DD – 0.3 V and 1 V. V_DD
may also be selected using REF0CN per SFR Definition 7.1. The electrical specifications for the Voltage
Reference are given in Table 7.1.
Vdd
To ADC Ref
Vref (external)
REF0CN[1:0]
2
Set REF0CN to:
00: Use external Vref
11: Use Vdd
Figure 7.1. Voltage Reference Functional Block Diagram
SFR Definition 7.1. REF0CN: Reference Control
R/W
R/W
R/W
R/W
R/W
R/W
-
-
-
-
-
-
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bits7–2: UNUSED. Read = 00000b; Write = don't care
Bit1–0:
REFSL1– REFSL0: Voltage reference selection.
Bits control which reference is selected.
00: External VREF source is selected.
01: Reserved.
10: Reserved.
11: V_DD selected as VREF source.
R/W
REFSL1
Bit1
R/W
Reset Value
REFSL0 00000000
Bit0 SFR Address:
0xD1
50
Rev. 1.6