PHP1 V4.0

This version of the display/stabiliser program is for the 
PIC16F84 or PIC16C84 microcontroller using a 4.000MHz 
crystal.

My transceiver has an I.F. frequency of 7.8000MHz. The 
required offsets are 7.79850MHz and 7.80150MHz for 
USB and LSB.  gadget40.asm is the source code for
the current version of the program used in both 
of my home made SSB transceivers.


The VFO/LO frequency is stored as a 24 bit binary number 
in registers  L_BYTE, M_BYTE and H_BYTE. 

In this version of the program, the IF offset is stored in 
registers COUNT1, COUNT2 and COUNT3.  (Note that COUNT1/2/3 
are also used by other parts of the program). 

To change the I.F. offset to a different value, locate 
the label CONVERT in the source code .  The code following 
this label adds/subtracts the I.F. offset to/from the 
VFO frequency.


For example:

ADD_HI	MOVLW	0X76		;STORE I.F. OFFSET. 
	MOVWF	COUNT1		;0BE776 HEX = 780150 Dec
	MOVLW	0XE7		;THIS IS THE BIT YOU NEED TO MODIFY -  
	MOVWF	COUNT2		;FOR A DIFFERENT IF OFFSET.
	MOVLW	0X0B
	MOVWF	COUNT3	
		
	MOVF	COUNT1,W	;ADD I.F. OFFSET TO FREQUENCY  
	ADDWF	L_BYTE,F	
	MOVF	COUNT2,W	
	BTFSC	STATUS,CARRY
	INCFSZ	COUNT2,W
	ADDWF	M_BYTE,F
	MOVF	COUNT3,W
	BTFSC	STATUS,CARRY
	INCFSZ	COUNT3,W
	ADDWF	H_BYTE,F	

adds 780150 to the VFO frequency.  780150 decimal = 0BE776 hexadecimal.

Note that the least significant byte is added first and the most 
significant byte is added last.


To save writing additional code for subtracting, the I.F.  is
subtracted by using a well know programmers trick. The subtraction 
is achieved by adding the 2's compliment of the I.F.  Adding -780150 
to a number has the same effect as subtracting +780150.

For example:

SUB_HI	MOVLW	0X8A		;STORE I.F. OFFSET. 
	MOVWF	COUNT1		;-780150 = 0XF4188A 
	MOVLW	0X18            ;THIS IS THE BIT YOU NEED TO MODIFY -
	MOVWF	COUNT2		;FOR A DIFFERENT IF OFFSET.
	MOVLW	0XF4
	MOVWF	COUNT3	
		
	MOVF	COUNT1,W	;SUBTRACT I.F. FROM FREQUENCY 
	ADDWF	L_BYTE,F	
	MOVF	COUNT2,W	
	BTFSC	STATUS,CARRY
	INCFSZ	COUNT2,W
	ADDWF	M_BYTE,F
	MOVF	COUNT3,W
	BTFSC	STATUS,CARRY
	INCFSZ	COUNT3,W
	ADDWF	H_BYTE,F

Subtracts 779850 from the VFO freq. by adding -779850 to the VFO freq.
-779850 = F419B6.   

I use a scientific calculator to do the decimal to hex conversion. When 
my trusty Sharp calculator gets lost under the junk pile, I use kCalc, 
a nice scientific calculator for the KDE desktop.  If you haven't yet 
made the change to Linux, you can use the Windows calculator.

This version of the program can subtract the IF from the VFO freq. 
or add the IF to the VFO freq.  I don't have any need to subtract 
the VFO frequency from the IF.  If you need to do this, it should 
be a fairly trivial programming exercise.  I know of at least one 
radio amateur who made this modification.  He has a 40M CW rig 
with a 12MHz I.F.  12 - 4.95 = 7.05



ASSEMBLING THE PROGRAM.
I tried assembling gadget40.asm on several different assemblers.
Gpasm for Linux assembles the file without any errors or warnings.
Mpasm for Dos or Windows assembles the file without any errors or warnings.

I had to make a few changes to the source code before I could assemble
it with Picalc for Dos.