PIC16F8X_13 Datasheet, PDF (53/128 Pages) Microchip Technology – 18-pin Flash/EEPROM 8-Bit Microcontrollers

8.12.3 WAKE-UP USING INTERRUPTS
When global interrupts are disabled (GIE cleared) and
any interrupt source has both its interrupt enable bit
and interrupt flag bit set, one of the following will occur:
• If the interrupt occurs before the execution of a
SLEEP instruction, the SLEEP instruction will com-
plete as a NOP. Therefore, the WDT and WDT
postscaler will not be cleared, the TO bit will not
be set and PD bits will not be cleared.
• If the interrupt occurs during or after the execu-
tion of a SLEEP instruction, the device will imme-
diately wake up from sleep. The SLEEP instruction
will be completely executed before the wake-up.
Therefore, the WDT and WDT postscaler will be
cleared, the TO bit will be set and the PD bit will
be cleared.
Even if the flag bits were checked before executing a
SLEEP instruction, it may be possible for flag bits to
become set before the SLEEP instruction completes. To
determine whether a SLEEP instruction executed, test
the PD bit. If the PD bit is set, the SLEEP instruction
was executed as a NOP.
To ensure that the WDT is cleared, a CLRWDT instruc-
tion should be executed before a SLEEP instruction.
8.13 Program Verification/Code Protection
If the code protection bit(s) have not been
programmed, the on-chip program memory can be
read out for verification purposes.
Note: Microchip does not recommend code pro-
tecting widowed devices.
8.14 ID Locations
Four memory locations (2000h - 2003h) are designated
as ID locations to store checksum or other code
identification numbers. These locations are not
accessible during normal execution but are readable
and writable only during program/verify. Only the
4 least significant bits of ID location are usable.
For ROM devices, these values are submitted along
with the ROM code.
PIC16F8X
8.15 In-Circuit Serial Programming
PIC16F8X microcontrollers can be serially
programmed while in the end application circuit. This is
simply done with two lines for clock and data, and three
other lines for power, ground, and the programming
voltage. Customers can manufacture boards with
unprogrammed devices, and then program the
microcontroller just before shipping the product,
allowing the most recent firmware or custom firmware
to be programmed.
The device is placed into a program/verify mode by
holding the RB6 and RB7 pins low, while raising the
MCLR pin from VIL to VIHH (see programming
specification). RB6 becomes the programming clock
and RB7 becomes the programming data. Both RB6
and RB7 are Schmitt Trigger inputs in this mode.
After reset, to place the device into programming/verify
mode, the program counter (PC) points to location 00h.
A 6-bit command is then supplied to the device, 14-bits
of program data is then supplied to or from the device,
using load or read-type instructions. For complete
details of serial programming, please refer to the
PIC16CXX Programming Specifications (Literature
#DS30189).
FIGURE 8-20: TYPICAL IN-SYSTEM SERIAL
PROGRAMMING
CONNECTION
External
Connector
Signals
+5V
0V
VPP
CLK
Data I/O
To Normal
Connections
PIC16FXX
VDD
VSS
MCLR/VPP
RB6
RB7
VDD
To Normal
Connections
For ROM devices, both the program memory and Data
EEPROM memory may be read, but only the Data
EEPROM memory may be programmed.
 1996-2013 Microchip Technology Inc.
DS30430D-page 53