Datasheet

PIC14000
DS40122B-page 76
Preliminary
 1996 Microchip Technology Inc.
10.2 Oscillator Confi
gurations
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, by 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 I
2
CSEL
SMBUS INCLKEN OSC2 OSC1
Read/Write
R/W R/W R/W R/W R/W R/W R/W R
POR value 00h 0
0 0 0 00 0X
Bit Name Function
B7 SMHOG
SMHOG enable
1 = Stretch I
2
C CLK signal (hold low) when receive data buffer is full (refer to
Section 7.5.4). For pausing I
2
C transfers while preventing interruptions of A/D
conversions.
0 = Disable I
2
C CLK stretch.
B6 SPGNDB
Serial Port Ground Select
1 = PORTD<1:0> ground reference is the RD5/AN5 pin.
0 = PORTD<1:0> ground reference is V
SS
.
B5 SPGNDA
Serial Port Ground Select
1 = PORTC<7:6> ground reference is the RA1/AN1 pin.
0 = PORTC<7:6> ground reference is V
SS
.
B4 I
2
CSEL
I
2
C Port select Bit.
1 = PORTD<1:0> are used as the I
2
C clock and data lines.
0 = PORTC<7:6> are used as the I
2
C clock and data lines.
B3 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.
B2 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.
B1 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.
B0 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.