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PIC18F2455/2550/4455/4550

22.9Analog Input Connection Considerations

A simplified circuit for an analog input is shown in Figure 22-4. Since the analog pins are connected to a digital output, they have reverse biased diodes to VDD and VSS. The analog input, therefore, must be between VSS and VDD. If the input voltage deviates from this

range by more than 0.6V in either direction, one of the diodes is forward biased and a latch-up condition may occur. A maximum source impedance of 10 kΩ is recommended for the analog sources. Any external component connected to an analog input pin, such as a capacitor or a Zener diode, should have very little leakage current.

FIGURE 22-4:

COMPARATOR ANALOG INPUT MODEL

 

 

 

VDD

 

 

RS < 10k

VT = 0.6V

RIC

 

 

 

 

 

Comparator

 

AIN

 

Input

 

 

ILEAKAGE

VA

CPIN

VT = 0.6V

5 pF

±500 nA

 

 

 

 

VSS

Legend: CPIN

=

Input Capacitance

VT

=

Threshold Voltage

ILEAKAGE =

Leakage Current at the pin due to various junctions

RIC

=

Interconnect Resistance

RS

=

Source Impedance

VA

=

Analog Voltage

 

 

 

TABLE 22-1: REGISTERS ASSOCIATED WITH COMPARATOR MODULE

 

 

 

 

 

 

 

 

 

Reset

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Values

 

 

 

 

 

 

 

 

 

on page

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CMCON

C2OUT

C1OUT

C2INV

C1INV

CIS

CM2

CM1

CM0

53

 

 

 

 

 

 

 

 

 

 

CVRCON

CVREN

CVROE

CVRR

CVRSS

CVR3

CVR2

CVR1

CVR0

53

INTCON

GIE/GIEH

PEIE/GIEL

TMR0IE

INT0IE

RBIE

TMR0IF

INT0IF

RBIF

51

PIR2

OSCFIF

CMIF

USBIF

EEIF

BCLIF

HLVDIF

TMR3IF

CCP2IF

54

PIE2

OSCFIE

CMIE

USBIE

EEIE

BCLIE

HLVDIE

TMR3IE

CCP2IE

54

IPR2

OSCFIP

CMIP

USBIP

EEIP

BCLIP

HLVDIP

TMR3IP

CCP2IP

54

PORTA

RA6(1)

RA5

RA4

RA3

RA2

RA1

RA0

54

LATA

LATA6(1)

LATA5

LATA4

LATA3

LATA2

LATA1

LATA0

54

TRISA

TRISA6(1)

TRISA5

TRISA4

TRISA3

TRISA2

TRISA1

TRISA0

54

Legend: — = unimplemented, read as ‘0’. Shaded cells are unused by the comparator module.

Note 1: PORTA<6> and its direction and latch bits are individually configured as port pins based on various oscillator modes. When disabled, these bits read as ‘0’.

2007 Microchip Technology Inc.

Preliminary

DS39632D-page 273

PIC18F2455/2550/4455/4550

NOTES:

DS39632D-page 274

Preliminary

2007 Microchip Technology Inc.

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