PIC14000 datasheet(76/153 Pages) MICROCHIP

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PIC14000

DS40122B-page 76

Preliminary

10.2

Oscillator Conﬁgurations

The PIC14000 can be operated with two different oscil-

lator options. The user can program a conﬁguration

word (CONFIG<0>) to select one of these:

• HS

High Speed Crystal/Ceramic Resonator

(CONFIG<0> =‘0’)

• IN

Internal oscillator (CONFIG<0> =‘1’)

(Default)

10.2.1

INTERNAL OSCILLATOR CIRCUIT

The PIC14000 includes an internal oscillator option

that offers additional cost and board-space savings. No

external components are required. The nominal

operating frequency is 4 MHz. The frequency is mea-

sured and stored into the calibration space in EPROM.

By selecting IN mode OSC1/PBTN becomes a digital

input (with weak internal pull-up resistor) and can be

read via bit MISC<0>. Writes to this location have no

effect. The OSC1/PBTN input is capable of generating

an interrupt to the CPU if enabled (Section 10.6). Also,

the OSC2 pin becomes a digital output for general pur-

pose use and is accessed via MISC<1>. Writes to this bit

directly affect the OSC2 pin. Reading this bit returns the

contents of the output latch. The MISC register format is

shown in Figure 10-2.

The OSC2 pin can also output the IN oscillator fre-

quency,

divided-by-four,

setting

INCLKEN

(MISC<2>).

Note:

The OSC2 output buffer provides less drive

than standard I/O.

FIGURE 10-2: MISC REGISTER

9Eh

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

MISC

SMHOG

SPGNDB SPGNDA

I2CSEL

SMBUS

INCLKEN

OSC2

OSC1

Read/Write

R/W

POR value 00h

Bit

Name

Function

SMHOG

SMHOG enable

1 = Stretch I2C CLK signal (hold low) when receive data buffer is full (refer to

Section 7.5.4). For pausing I2C transfers while preventing interruptions of A/D

conversions.

0 = Disable I2C CLK stretch.

SPGNDB

Serial Port Ground Select

1 = PORTD<1:0> ground reference is the RD5/AN5 pin.

0 = PORTD<1:0> ground reference is VSS.

SPGNDA

Serial Port Ground Select

1 = PORTC<7:6> ground reference is the RA1/AN1 pin.

0 = PORTC<7:6> ground reference is VSS.

I2CSEL

I2C Port select Bit.

1 = PORTD<1:0> are used as the I2C clock and data lines.

0 = PORTC<7:6> are used as the I2C clock and data lines.

SMBus

SMBus-Compatibility Select

1 = SMBus compatibility mode is enabled. PORTC<7:6> and PORTD<1:0> have

SMBus-compatible input thresholds.

0 = SMBus-compatibility is disabled. PORTC<7:6> and PORTD<1:0> have Schmitt Trig-

ger input thresholds.

INCLKEN

Oscillator Output Select (available in IN mode only).

1 = Output IN oscillator signal divided by four on OSC2 pin.

0 = Disconnect IN oscillator signal from OSC2 pin.

OSC2

OSC2 output port bit (available in IN mode only).

Writes to this location affect the OSC2 pin in IN mode. Reads return the value of the

output latch.

OSC1

OSC1 input port bit (available in IN mode only).

Reads from this location return the status of the OSC1 pin in IN mode. Writes have no

effect.

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