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PIC16F84A Datasheet(PDF) 62 Page - Microchip Technology |
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PIC16F84A Datasheet(HTML) 62 Page - Microchip Technology |
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62 / 68 page  PIC16F84A DS35007A-page 62 Preliminary © 1998 Microchip Technology Inc. APPENDIX C: MIGRATION FROM BASELINE TO MIDRANGE DEVICES This section discusses how to migrate from a baseline device (i.e., PIC16C5X) to a midrange device (i.e., PIC16CXXX). The following is the list of feature improvements over the PIC16C5X microcontroller family: 1. Instruction word length is increased to 14 bits. This allows larger page sizes both in program memory (2K now as opposed to 512 before) and the register file (128 bytes now versus 32 bytes before). 2. A PC latch register (PCLATH) is added to handle program memory paging. PA2, PA1 and PA0 bits are removed from the status register and placed in the option register. 3. Data memory paging is redefined slightly. The STATUS register is modified. 4. Four new instructions have been added: RETURN , RETFIE, ADDLW, and SUBLW. Two instructions, TRIS and OPTION, are being phased out although they are kept for compatibility with PIC16C5X. 5. OPTION and TRIS registers are made addressable. 6. Interrupt capability is added. Interrupt vector is at 0004h. 7. Stack size is increased to 8 deep. 8. Reset vector is changed to 0000h. 9. Reset of all registers is revisited. Five different reset (and wake-up) types are recognized. Registers are reset differently. 10. Wake up from SLEEP through interrupt is added. 11. Two separate timers, the Oscillator Start-up Timer (OST) and Power-up Timer (PWRT), are included for more reliable power-up. These timers are invoked selectively to avoid unnecessary delays on power-up and wake-up. 12. PORTB has weak pull-ups and interrupt on change features. 13. T0CKI pin is also a port pin (RA4/T0CKI). 14. FSR is a full 8-bit register. 15. "In system programming" is made possible. The user can program PIC16CXX devices using only five pins: VDD, VSS, VPP, RB6 (clock) and RB7 (data in/out). To convert code written for PIC16C5X to PIC16F84A, the user should take the following steps: 1. Remove any program memory page select operations (PA2, PA1, PA0 bits) for CALL, GOTO. 2. Revisit any computed jump operations (write to PC or add to PC, etc.) to make sure page bits are set properly under the new scheme. 3. Eliminate any data memory page switching. Redefine data variables for reallocation. 4. Verify all writes to STATUS, OPTION, and FSR registers since these have changed. 5. Change reset vector to 0000h. |
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