PIC16C745/765
keep the chip in reset until the crystal oscillator is stable.
The other is the Power-up Timer (PWRT), which pro-
vides a fixed delay of 72 ms (nominal) on power-up only
and is designed to keep the part in reset, while the
power supply stabilizes. With these two timers on-chip,
most applications need no external reset circuitry.
13.0 SPECIAL FEATURES OF THE
CPU
What sets a microcontroller apart from other proces-
sors are special circuits to deal with the needs of real-
time applications. The PIC16C745/765 family has a
host of such features intended to maximize system reli-
ability, minimize cost through elimination of external
components, provide power saving operating modes
and offer code protection. These are:
SLEEP mode is designed to offer a very low current
power-down mode. The user can wake-up from SLEEP
through external reset, WDT wake-up or through an
interrupt. Several oscillator options are also made
available to allow the part to fit the application. The EC
oscillator allows the user to directly drive the microcon-
troller, while the HS oscillator allows the use of a high
speed crystal/resonator. A set of configuration bits are
used to select various options.
• Oscillator selection
• Reset
- Power-on Reset (POR)
- Power-up Timer (PWRT)
- Oscillator Start-up Timer (OST)
- Brown-out Reset (BOR)
• Interrupts
13.1
Configuration Bits
The configuration bits can be programmed (read as '0')
or left unprogrammed (read as '1') to select various
device configurations. These bits are mapped in pro-
gram memory location 2007h.
• Watchdog Timer (WDT)
• SLEEP
• Code protection
• ID locations
The user will note that address 2007h is beyond the user
program memory space. In fact, it belongs to the special
test/configuration memory space (2000h - 3FFFh),
which can be accessed only during programming.
• In-Circuit Serial Programming™ (ICSP)
The PIC16C745/765 has a Watchdog Timer, which can
be shut off only through configuration bits. It runs off its
own dedicated RC oscillator for added reliability. There
are two timers that offer necessary delays on power-up.
One is the Oscillator Start-up Timer (OST), intended to
REGISTER 13-1: CONFIGURATION WORD
CP1
CP0
CP1
CP0
CP1
CP0
—
—
CP1
CP0 PWRTE WDTE FOSC1 FOSC0
bit0
Register: CONFIG
Address 2007h
bit13
bit 13-12: CP<1:0>: Code Protection bits(1)
11-10: 00= All memory is code protected
9-8: 01= Upper 3/4th of program memory code protected
5-4: 10= Upper half of program memory code protected
11= Code protection off
bit 7-6: Unimplemented: Read as ’1’
bit 3:
PWRTE: Power-up Timer Enable bit
1 = PWRT disabled • No delay after Power-up reset or Brown-out reset
0 = PWRT enabled • A delay of 4x WDT (72 ms) is present after Power-up and Brown-out
bit 2:
WDTE: Watchdog Timer Enable bit
1 = WDT enabled
0 = WDT disabled
bit 1-0: FOSC<1:0>: Oscillator Selection
00- HS- HS osc
01- EC- External clock. CLKOUT on OSC2 pin
10- H4- HS osc with 4x PLL enabled
11- E4- External clock with 4x PLL enabled. CLKOUT on OSC2 pin
Note 1: All of the CP<1:0> pairs have to be given the same value to enable the code protection scheme listed.
1999 Microchip Technology Inc.
Advanced Information
DS41124A-page 95
MICROCHIP [ MICROCHIP ]
