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PIC16F84A Datasheet(PDF) 52 Page - Microchip Technology |
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PIC16F84A Datasheet(HTML) 52 Page - Microchip Technology |
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52 / 124 page  PIC16F8X DS30430C-page 52 © 1998 Microchip Technology Inc. 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 immedi- ately 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. 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. 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 For ROM devices, both the program memory and Data EEPROM memory may be read, but only the Data EEPROM memory may be programmed. Note: Microchip does not recommend code pro- tecting widowed devices. External Connector Signals To Normal Connections To Normal Connections PIC16FXX VDD VSS MCLR/VPP RB6 RB7 +5V 0V VPP CLK Data I/O VDD |
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