P12C508 Microchip Technology, P12C508 Datasheet - Page 28

• Manufacturer Part Number: P12C508
• Description: 8-Pin / 8-Bit CMOS Microcontroller
• Manufacturer: Microchip Technology

PIC12C5XX
FIGURE 7-6:
7.2.5
The internal RC oscillator provides a fixed 4 MHz (nom-
inal) system clock.
In addition, a calibration instruction is programmed into
the top of memory which indicates the calibration value
for the internal RC oscillator. This value, OSCCAL, is
programmed as a MOVLW XX instruction where XX is the
calibration value, and is placed at the reset vector. This
will load the W register with the calibration value upon
reset and the PC will then roll over to 0x000. The user
then has the option of writing the value to the OSCCAL
Register (05h) or ignoring it.
TABLE 7-3:
DS40139A-page 28
Legend: u = unchanged, x = unknown, - = unimplemented bit, read as ‘0’, ? = value depends on condition.
Note 1:
Note 2:
Cext
V
Rext
SS
V
FSR (12C508)
FSR (12C509)
DD
INTERNAL 4 MHZ RC OSCILLATOR
OSCCAL
Register
STATUS
OPTION
TMR0
GPIO
INDF
TRIS
Bits <7:4> of W register contain oscillator calibration (OSCCAL) values due to MOVLW XX instruction at
top of memory.
See Table 7-6 for reset value for specific conditions
PC
W
RC OSCILLATOR MODE
RESET CONDITIONS FOR REGISTERS
OSC1
N
Address
PIC12C5XX
00h
01h
02h
03h
04h
04h
05h
06h
—
—
—
Advance Information
Internal
clock
7.3
The device differentiates between various kinds of
reset:
a) Power on reset (POR)
b) MCLR reset during normal operation
c) MCLR reset during SLEEP
d) WDT time-out reset during normal operation
e) WDT time-out reset during SLEEP
f) Wake-up from SLEEP on pin change
Some registers are not reset in any way; they are
unknown on POR and unchanged in any other reset.
Most other registers are reset to “reset state” on power-
on reset (POR), on MCLR or WDT reset during normal
operation . They are not affected by a WDT reset during
SLEEP or MCLR reset during SLEEP, since these
resets are viewed as resumption of normal operation.
The exceptions to this are TO, PD, and GPWUF bits.
They are set or cleared differently in different reset sit-
uations. These bits are used in software to determine
the nature of reset. See Table 7-3 for a full description
of reset states of all registers.
Power-on Reset
qqqq xxxx (1)
xxxx xxxx
xxxx xxxx
1111 1111
0001 1xxx
111x xxxx
110x xxxx
0111 ----
--xx xxxx
1111 1111
--11 1111
RESET
1996 Microchip Technology Inc.
Wake-up on Pin Change
qqqq uuuu (1)
?00? ?uuu (2)
WDT time-out
MCLR Reset
uuuu uuuu
uuuu uuuu
1111 1111
111u uuuu
11uu uuuu
uuuu ----
--uu uuuu
1111 1111
--11 1111