PIC16C72-04SLASHSP datasheet(57/124 Pages) MICROCHIP

57 / 124 page

PIC16C72 Series

Preliminary

DS39016A-page 57

9.2

Selecting the A/D Conversion Clock

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

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

The source of the A/D conversion clock is software

selectable. The four possible options for TAD are:

• 2TOSC

• 8TOSC

• 32TOSC

• Internal 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 9-1 shows the resultant TAD times derived from

the device operating frequencies and the A/D clock

source selected.

9.3

Configuring Analog Port Pins

The ADCON1, TRISA, and TRISE registers control the

operation of the A/D port pins. The port pins that are

desired as analog inputs must have their correspond-

ing TRIS bits set (input). If the TRIS bit is cleared (out-

put), 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.

TABLE 9-1

TAD vs. DEVICE OPERATING FREQUENCIES

Note 1: When reading the port register, all pins

conﬁgured as analog input channels 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 AN4:AN0

pins), may cause the input buffer to con-

sume current that is out of the devices

speciﬁcation.

AD Clock Source (TAD)

Device Frequency

Operation

ADCS1:ADCS0

20 MHz

5 MHz

1.25 MHz

333.33 kHz

2TOSC

100 ns(2)

400 ns(2)

1.6

µs

8TOSC

400 ns(2)

1.6

µs

6.4

µs

µs(3)

32TOSC

1.6

µs

6.4

µs

25.6

µs(3)

RC(5)

2 - 6

µs(1,4)

2 - 6

µs(1,4)

2 - 6

µs(1,4)

2 - 6

µs(1)

Legend: Shaded cells are outside of recommended range.

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: When device frequency is greater than 1 MHz, the RC A/D conversion clock source is recommended for

sleep operation only.

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

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