Changing Micros


Chapter 1         Chapter 2         Chapter 3       Chapter 4

Chapter 5

At some stage in your work you will have to change micro's. It may be to change from a "One Time Programmable" chip to a flash version, or it may be to a chip with more features, such as Analogue to Digital Conversion.
Or it may be to our low-cost MCV08A - with 1k of program, 1 - ADC and precision 0.6v reference.
Changing from one chip to another is not easy as the files (the files you use to store temporary data during the running of a program) start at different addresses.
That's why this information is important, so you can plan ahead and make the transfer as simple as possible.
At the start of a program we use "equates."
This is simply assigning each name used in the program, to a file.
Suppose we create a delay sub-routine. Suppose it requires two files. We call them: "del1" and "del2" (for delay1 and delay2).
For a PIC micro with the code: MCV08A, the first available file is 0Ah. For a PIC12F629, the first available file is 20h and for a PIC12F508/9, it is 07h, as shown in the file map:

Since the General Purpose Registers start at different locations, del1 and del2 will be file 0Ah, and 0Bh for the MCV08A and different numbers for the other two chips. To save moving all the files when changing chips, we have a simple way to make all files "automatically change."

Up to now, we have advocated using "equates" to assign each file-name to one of the General Purpose Registers, thus:

timera		equ	20h	;general purpose timer
timerb		equ	21h	;general purpose timer
timerc		equ	22h	;general purpose timer
timerd		equ	23h	;general purpose timer
note_select	equ	24h	;selection of note
note_tone	equ	25h	;frequency of note
note_length	equ	26h	;length of note
note_tempo	equ	27h	;tempo of song
random		equ	28h	;random number

All the file numbers will have to be moved when changing micro's. To save this, and prevent any mistakes we use cblock. This is a directive used for defining files in a compact way. The format of cblock is:

cblock 0x20    ;define the start of the files. The first "file" or "register" for a 12F629 is 20h
timera            ;this will be file 20h
timerb            ;this will be file 21h
timerc            ;this will be file 22h etc etc etc

endc

Each file on the list will be allocated the next General Purpose Register.

To make cblock universal, we use:

cblock  RAMStart

The assembler will automatically equate the names you have used for your sub-routines with the start of the General Purpose Registers. For MCV08A, this will be 0Ah, and for PIC12F629 it will be 20h, etc.

cblock becomes:

cblock RAMStart

timera		
timerb		
timerc		
timerd		
note_select	
note_tone	
note_length	
note_tempo	
random

endc


The next things to consider are the different features of each chip:

1. The MCV08A, PIC12F629 and PIC12C509 has 1k of program-space, the PIC12C508A has 512 spaces.

2. The MCV08A and PIC12C508/9 has no EEPROM and cannot store data when the chip is turned off.

3. All chips have the same pin numbers for GP0, GP1, GP2, GP3, GP4 and GP5. All outputs sink and source 25mA max.

4. THE STACK   MCV08A and PIC12C508/9 has a 2-stack. This allows a call to be made to a sub-routine and the sub-routine can make a call to another sub-routine. PIC12F629 has an 8-stack and any programs to be transferred from this chip to either of the others will have to be carefully checked to determine how the calls have been made.

5. MCV08A has no interrupt feature. For instance, if you want the micro to go to "isr" (Interrupt Service Routine) when it overflows from FF to 00, do not use the MCV08A.
 

cvcc



12-Bit PSEUDO Instruction Mnemonics 

Mnemonic
Description
Equivalent
Operation(s)
Status
(file 03h)
ADDCF
f,d
Add Carry to File
BTFSC
INCF
03h,0
f,d
Z
ADDDCF
f,d
Add Digit Carry to File
BTFSC
INCF
03h,1
f,d
Z
B
k
Branch
GOTO
k
-
BC
k
Branch on Carry
BTFSC
GOTO
03h,0
k
-
BDC
k
Branch on Digit Carry
BTFSC
GOTO
03h,1
k
-
BNC
k
Branch on No Carry
BTFSS
GOTO
03h,0
k
-
BNDC
k
Branch on No Digit Carry
BTFSS
GOTO
03h,1
k
-
BNZ
k
Branch on No Zero
BTFSS
GOTO
03h,2
k
-
BZ
k
Branch on Zero
BTFSC
GOTO
03h,2
k
-
CLRC
 
Clear Carry
BCF
03h,0
-
CLRDC
 
Clear Digit Carry
BCF
03h,1
-
CLRZ
 
Clear Zero
BCF
03h,2
-
LCALL
k
Long Call
BCF/BSF
BCF/BSF
CALL
0Ah,3
0Ah,4
k
 
LGOTO
k
Long GOTO
BCF/BSF
BCF/BSF
GOTO
0Ah,3
0Ah,4
k
 
MOVFW
f
Move File to W
MOVF
f,0
Z
NEGF
f,d
Negate File
COMF
INCF
f,1
f,d
Z
SETC
 
Set Carry
BSF
03h,0
-
SETDC
 
Set Digit Carry
BSF
03h,1
-
SETZ
 
Set Zero
BSF
03h,2
-
SKPC
 
Skip on Carry
BTFSS
03h,0
-
SKPDC
 
Skip on Digit Carry
BTFSS
03h,1
-
SKPNC
 
Skip on No Carry
BTFSC
03h,0
-
SKPNDC
 
Skip on No Digit Carry
BTFSC
03h,1
-
SKPNZ
 
Skip on Non Zero
BTFSC
03h,2
-
SKPZ
 
Skip on Zero
BTFSS
03h,2
-
SUBCF
f,d
Subtract Carry from File
BTFSC
DECF
03h,0
f,d
Z
SUBDCF
f,d
Subtract Digit Carry from File
BTFSC
DECF
03h,1
f,d
Z
TSTF
f
Test File
MOVF
f,1
Z

 



 
1/2/08