MCP25020ISLASHP datasheet(41/66 Pages) MICROCHIP

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DS21664D-page 41

MCP2502X/5X

7.0

ANALOG-TO-DIGITAL

CONVERTER (A/D) MODULE

7.1

Description

The Analog-to-Digital (A/D) module is a four-channel,

10-bit successive approximation type of A/D. The A/D

allows conversion of an analog input signal to a

corresponding 10-bit number. The four channels are

multiplexed on the GP[3:0] pins. The converter is

turned off/on via the ADCON0 register and each

channel is individually enabled via the ADCON1 control

selectable as internal or external. Each channel can be

set to one of two conversion modes:

Auto-conversion

Convert-on-request.

7.2

A/D Module Registers

The A/D module itself has several registers. The

registers are:

• A/D Control Register 0 (ADCON0)

• A/D Control Register 1 (ADCON1)

• Transmit-on-Change Register (IOINTEN)

• Compare and Polarity Register (ADCMPnL)

• A/D Result Registers (ADRESnL, ADRESnH)

The ADCON0 register controls the operation of the

A/D module, including auto-conversion rate and enable

bit. The ADCON1 register enables the A/D function on

port pins GP3:GP0, A/D conversion rate and selects

the voltage reference source. The IOINTEN register’s

four least significant bits enable/disable the transmit-

on-change function. The ADCMPnL.ADPOL bit sets

the polarity (above or below threshold) for the transmit-

on-change function.

The result of an A/D conversion is made available to

the user within the data field of the Read A/D Registers

output message via the CAN bus. This message can

be directly requested by another CAN node or be

automatically transmitted (TXIDO), as has been

described previously.

Additionally, the individual channel results may be read

using the “Read Register” command as described in

Section 4.3.1 “Information Request Messages” and

as shown in Table 3-2 by addressing the appropriate

A/D result register (ADRESnL and ADRESnH).

7.3

A/D Conversion Modes

There are two modes of conversion that can be

individually selected for each analog channel that has

been

enabled.

These

are

auto-conversion

and

conversion-on-request.

7.3.1

AUTO-CONVERSION MODE

If the Auto-conversion mode is selected (STCON), an

A/D conversion is performed sequentially for each

channel that has been set to Analog Input mode and

has been configured for Auto-conversion mode.

Conversion starts with AN0 and is immediately

followed by AN1, etc. Once the conversion has

completed, the value is stored in the analog channel

registers for the respective channel.

The rate of the auto-conversion is determined by a

timer and prescaler. The formula for determining

conversion rates is:

Typical conversion rates with a 20 MHz oscillator input

are shown in Table 7-1.

TABLE 7-1:

AUTO-CONVERSION RATES

FOR GIVEN PRESCALE

RATES AT 20 MHZ

The timer is turned on if one of the GPnTXC bits are set

in the IOINTEN register and configured as analog

input.

The prescaler counter is cleared when the device is

reset (RST reset or Power-on reset).

Note:

The GPDDR register controls the direction

of the GPIO pins, even when they are

being used as analog inputs. The user

must ensure that the bits in the GPDDR

using them as analog inputs.

TOPS[2:0]

Prescale

Rate

Auto-Conversion

Rate

000

1:1

51 µs

001

1:8

410 µs

010

1:32

2 ms

011

1:128

7 ms

100

1:512

26 ms

101

1:1024

52 ms

110

1:2048

105 ms

111

1:4096

210 ms

OSC

() 1024

() Prescaler rate

()

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