PIC12CE673-04SLASHP datasheet(41/116 Pages) MICROCHIP

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Preliminary

DS40181B-page 41

PIC12CE67X

8.2

Selecting the A/D Conversion Clock

The A/D conversion time per bit is deﬁned as TAD. The

A/D conversion requires 9.5 TAD per 8-bit conversion.

The source of the A/D conversion clock is software

selected. The four possible options for TAD are:

• 2TOSC

• 8TOSC

• 32TOSC

• Internal ADC RC oscillator

For correct A/D conversions, the A/D conversion clock

(TAD) must be selected to ensure a minimum TAD time

of 1.6

µs.

Table 8-1 shows the resultant TAD times derived from

the device operating frequencies and the A/D clock

source selected.

8.3

Configuring Analog Port Pins

The ADCON1 and TRIS registers control the operation

of the A/D port pins. The port pins that are desired as

analog inputs must have their corresponding TRIS bits

set (input). If the TRIS bit is cleared (output), the digital

output level (VOH or VOL) will be converted.

The A/D operation is independent of the state of the

CHS2:CHS0 bits and the TRIS bits.

Note 1: When reading the port register, all pins

conﬁgured as analog input channel will

read as cleared (a low level). Pins conﬁg-

ured as digital inputs, will convert an ana-

log input. Analog levels on a digitally

conﬁgured input will not affect the conver-

sion accuracy.

Note 2: Analog levels on any pin that is deﬁned as

a digital input (including the AN3:AN0

pins), may cause the input buffer to con-

sume current that is out of the devices

speciﬁcation.

TABLE 8-1:

TAD vs. DEVICE OPERATING FREQUENCIES

AD Clock Source (TAD)

Device Frequency

Operation

ADCS1:ADCS0

4 MHz

1.25 MHz

333.33 kHz

2TOSC

500 ns(2)

1.6

µs

8TOSC

2.0

µs

6.4

µs

µs(3)

32TOSC

8.0

µs

25.6

µs(3)

Internal ADC RC Oscillator(5)

2 - 6

µs(1,4)

2 - 6

µs(1,4)

2 - 6

µs(1)

Note 1: The RC source has a typical TAD time of 4

µs.

2: These values violate the minimum required TAD time.

3: For faster conversion times, the selection of another clock source is recommended.

4: While in RC mode, with device frequency above 1 MHz, conversion accuracy is out of speciﬁcation.

5: For extended voltage devices (LC), please refer to Electrical Speciﬁcations section.

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