C8051F340 View Datasheet(PDF) - Unspecified

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C8051F340

Full Speed USB Flash MCU Family

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C8051F340/1/2/3/4/5/6/7

5.1. Analog Multiplexer

AMUX0 selects the positive and negative inputs to the ADC. The positive input (AIN+) can be connected to

individual Port pins, the on-chip temperature sensor, or the positive power supply (VDD). The negative

input (AIN-) can be connected to individual Port pins, VREF, or GND. When GND is selected as the neg-

ative input, ADC0 operates in Single-ended Mode; at all other times, ADC0 operates in Differential

Mode. The ADC0 input channels are selected in the AMX0P and AMX0N registers as described in SFR

Definition 5.1 and SFR Definition 5.2.

The conversion code format differs between Single-ended and Differential modes. The registers ADC0H

and ADC0L contain the high and low bytes of the output conversion code from the ADC at the completion

of each conversion. Data can be right-justified or left-justified, depending on the setting of the AD0LJST bit

(ADC0CN.0). When in Single-ended Mode, conversion codes are represented as 10-bit unsigned integers.

Inputs are measured from ‘0’ to VREF x 1023/1024. Example codes are shown below for both right-justi-

fied and left-justified data. Unused bits in the ADC0H and ADC0L registers are set to ‘0’.

Input Voltage

(Single-Ended)

VREF x 1023/1024

VREF x 512/1024

VREF x 256/1024

0

Right-Justified ADC0H:ADC0L

(AD0LJST = 0)

0x03FF

0x0200

0x0100

0x0000

Left-Justified ADC0H:ADC0L

(AD0LJST = 1)

0xFFC0

0x8000

0x4000

0x0000

When in Differential Mode, conversion codes are represented as 10-bit signed 2’s complement numbers.

Inputs are measured from –VREF to VREF x 511/512. Example codes are shown below for both right-jus-

tified and left-justified data. For right-justified data, the unused MSBs of ADC0H are a sign-extension of the

data word. For left-justified data, the unused LSBs in the ADC0L register are set to ‘0’.

Input Voltage

(Differential)

VREF x 511/512

VREF x 256/512

0

–VREF x 256/512

–VREF

Right-Justified ADC0H:ADC0L

(AD0LJST = 0)

0x01FF

0x0100

0x0000

0xFF00

0xFE00

Left-Justified ADC0H:ADC0L

(AD0LJST = 1)

0x7FC0

0x4000

0x0000

0xC000

0x8000

Important Note About ADC0 Input Configuration: Port pins selected as ADC0 inputs should be config-

ured as analog inputs, and should be skipped by the Digital Crossbar. To configure a Port pin for analog

input, set to ‘0’ the corresponding bit in register PnMDIN (for n = 0,1,2,3). To force the Crossbar to skip a

Port pin, set to ‘1’ the corresponding bit in register PnSKIP (for n = 0,1,2). See Section “15. Port Input/

Output” on page 147 for more Port I/O configuration details.

42

Rev. 0.5

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