PIC Tutorial Changes
Changes for the PIC16F876 board
The
PIC16F876 is very similar to the 16F628, and uses the same 14 bit command
set, so the differences are pretty small, but a few changes to the
existing tutorial code is required.
- Initialisation code - the processor type, include file, and configuration fuse settings need changing.
- Setup code - the 16F628 requires the CMCON register setting to disable the comparator hardware, the 16F876 doesn't have this (although the 16F876A does, but isn't set by default). However, the 16F876 does have PortA set as analogue inputs by default, so these require setting as digital inputs in the setup code.
- Delay routines - as we're running the 16F876 five times as fast, the delay routines require modifying to use five times as many cycles.
- PORT changes - the 16F628 has two 8-bit ports A and B, the 16F876 has three ports - but only B and C are 8-bit, port A only has 6 pins available RA0-RA5, five of the six can be used as analogue inputs. So it's probably easiest to change all references to PortA and TrisA to PortC and TrisC, and connect to PortC in place of PortA.
| PIC16F628-4MHz | PIC16F876-20MHz |
| Initialisation code | |
| LIST p=16F628 include "P16F628.inc" __config 0x3D18 |
LIST p=16F876 include "P16F876.inc" __config 0x393A |
|
Setup code |
|
| movlw 0x07 movwf CMCON |
BANKSEL ADCON1 movlw 0x06 movwf ADCON1 BANKSEL PORTA |
|
Delay routines |
|
Delay255 movlw 0xff ;delay 255mS goto d0 Delay100 movlw d'100' ;delay 100mS goto d0 Delay50 movlw d'50' ;delay 50mS goto d0 Delay20 movlw d'20' ;delay 20mS goto d0 Delay10 movlw d'10' ;delay 10mS goto d0 Delay1 movlw d'1' ;delay 1mS goto d0 Delay5 movlw 0x05 ;delay 5ms d0 movwf count1 d1 movlw 0xC7 movwf counta movlw 0x01 movwf countb Delay_0 decfsz counta, f goto $+2 decfsz countb, f goto Delay_0 decfsz count1 ,f goto d1 retlw 0x00 |
Delay255 movlw 0xff ;delay 255mS goto d0 Delay100 movlw d'100' ;delay 100mS goto d0 Delay50 movlw d'50' ;delay 50mS goto d0 Delay20 movlw d'20' ;delay 20mS goto d0 Delay10 movlw d'10' ;delay 10mS goto d0 Delay1 movlw d'1' ;delay 1mS goto d0 Delay5 movlw 0x05 ;delay 5ms d0 movwf count1 d1 movlw 0xE7 movwf counta movlw 0x04 movwf countb Delay_0 decfsz counta, f goto $+2 decfsz countb, f goto Delay_0 decfsz count1 ,f goto d1 retlw 0x00 |
|
PORT changes |
|
| TRISA PORTA |
TRISC PORTC |
The
changes above should allow the existing 16F628 tutorials to work on the
16F876 board, however the 16F876 has greater hardware capabilities than
the 16F628, for example - 5x10 bit analogue inputs and two PWM outputs,
both of these will be used in later tutorials, and will obviously not be
possible on the 16F628.