PIC16F676-ESLASHST datasheet(42/132 Pages) MICROCHIP

42 / 132 page

PIC16F630/676

DS40039F-page 42

 2010 Microchip Technology Inc.

6.3

Analog Input Connection

Considerations

A simplified circuit for an analog input is shown in

Figure 6-3. 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 may occur. A

maximum

source

impedance

10 k



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 6-3:

ANALOG INPUT MODE

6.4

Comparator Output

The comparator output, COUT, is read through the

CMCON register. This bit is read-only. The comparator

output may also be directly output to the RA2 pin in

three of the eight possible modes, as shown in

Figure 6-2. When in one of these modes, the output on

RA2 is asynchronous to the internal clock. Figure 6-4

shows the comparator output block diagram.

The TRISA<2> bit functions as an output enable/

disable for the RA2 pin while the comparator is in an

Output mode.

FIGURE 6-4:

MODIFIED COMPARATOR OUTPUT BLOCK DIAGRAM

Rs < 10K

AIN

CPIN

5 pF

VDD

VT = 0.6V

RIC

Leakage

±500 nA

Vss

Legend:

CPIN

= Input Capacitance

= Threshold Voltage

ILEAKAGE

= Leakage Current at the pin due to Various Junctions

RIC

= Interconnect Resistance

= Source Impedance

= Analog Voltage

Note 1: When reading the PORTA register, all

pins configured as analog inputs will read

as a ‘0’. Pins configured as digital inputs

will convert an analog input according to

the TTL input specification.

2: Analog levels on any pin that is defined as

a digital input, may cause the input buffer

to consume more current than is

specified.

To RA2/T0CKI pin

RD CMCON

Set CMIF bit

Reset

To Data Bus

CINV

CVREF

RD CMCON

RA1/CIN-

RA0/CIN+

CM2:CM0

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