PIC18F258-ESLASHLSQTP datasheet(253/402 Pages) MICROCHIP

253 / 402 page

DS41159E-page 251

PIC18FXX8

21.2

Comparator Operation

A single comparator is shown in Figure 21-2 along with

the relationship between the analog input levels and

the digital output. When the analog input at VIN+ is less

than the analog input VIN-, the output of the comparator

is a digital low level. When the analog input at VIN+ is

greater than the analog input VIN-, the output of the

comparator is a digital high level. The shaded areas of

the output of the comparator in Figure 21-2 represent

the uncertainty due to input offsets and response time.

21.3

Comparator Reference

An external or internal reference signal may be used

depending on the comparator operating mode. The

analog signal present at VIN- is compared to the signal

at VIN+ and the digital output of the comparator is

adjusted accordingly (Figure 21-2).

FIGURE 21-2:

SINGLE COMPARATOR

21.3.1

EXTERNAL REFERENCE SIGNAL

When external voltage references are used, the

comparator module can be configured to have the com-

parators operate from the same or different reference

sources. However, threshold detector applications may

require the same reference. The reference signal must

be between VSS and VDD and can be applied to either

pin of the comparator(s).

21.3.2

INTERNAL REFERENCE SIGNAL

The comparator module also allows the selection of an

internally generated voltage reference for the compara-

tors. Section 22.0 “Comparator Voltage Reference

Module” contains a detailed description of the module

that provides this signal. The internal reference signal is

used when comparators are in mode CM<2:0> = 110

(Figure 21-1). In this mode, the internal voltage

reference is applied to the VIN+ pin of both comparators.

21.4

Comparator Response Time

Response time is the minimum time, after selecting a

new reference voltage or input source, before the

comparator output has a valid level. If the internal ref-

erence is changed, the maximum delay of the internal

voltage reference must be considered when using the

comparator outputs. Otherwise, the maximum delay of

the comparators should be used (Section 27.0

“Electrical Characteristics”).

21.5

Comparator Outputs

The comparator outputs are read through the CMCON

outputs may also be directly output to the RE1 and RE2

I/O pins. When enabled, multiplexors in the output path

of the RE1 and RE2 pins will switch and the output of

each pin will be the unsynchronized output of the

comparator.

The

uncertainty

each

the

comparators is related to the input offset voltage and

the

response

time

given

the

specifications.

Figure 21-3 shows the comparator output block

diagram.

The TRISE bits will still function as an output enable/

disable for the RE1 and RE2 pins while in this mode.

The polarity of the comparator outputs can be changed

using the C2INV and C1INV bits (CMCON<4:5>).

VIN+

VIN-

Output

VIN–

VIN+

Output

VIN+

VIN-

Note 1: When reading the Port 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

Schmitt Trigger input specification.

2: Analog levels on any pin defined as a dig-

ital input may cause the input buffer to

consume more current than is specified.

PIC18F258-E/LSQTP Datasheet(PDF) 253 Page - Microchip Technology

PIC18F258-E/LSQTP Datasheet(HTML) 253 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL