;**********************************************************
;*  blink.asm
;* Small demo program 
;* for the SALT 16F876 board. Blinks light attached to c0.
;**********************************************************
;*  Uses an inner and an outer loop structure to achieve
;*  a delay long enough to see the blink on LED indicators.
;*  
;* Walt Bankes, 2002
;**********************************************************
;**********************************************************
;*  BOARD DESCRIPTION - SALT 16F876 board
;*  including some instructions
;*  usually necessary for the operation of this board.
;*
;*	Some connections to this board may seem strange to
;*	an experienced board designer. Most of these 
;*	strange "features" are manifestations of trade offs
;*	required to place all of the traces on one side of
;*	the printed circuit board without resorting to 
;*	jumper wires.
;*	It appears 18FXXXX PICs will be available sometime
;*	soon that are pin compatable with the 16F876. They
;*	will probably allow this board to be used more
;*	readily with higher level languages since the
;*	18 series parts have an architecture and more 
;* 	memory specifically to accomodate that.
;**********************************************************
;*  Power supply options:
;*   +5v. DC is required to power the micro controller.
;*
;*   	5 volts may be supplied externally through board pins
;*	1 and 2. If you choose that option four parts may
;*	be left off of the board - the power connector, the
;*	bridge recifier, the 5 v regulator, and the 470 uf cap.
;*
;*	By installing the power supply parts mentioned above
;*	you may connect a wide variety of "wall wart" supplies
;*	to the board. In which case you will have +5 volts
;*	available on board pins 1 and 2 to power experiments.
;*	The range of power supplies acceptable are from
;*	6 to 12 volts AC or 9 to 18 volts DC of either polarity.
;*
;*   Edge Connector Pin assignments:(Viewed left to right
;*   from the switch edge of the top of the board).
;*	
;* 1	GND
;* 2	+5v
;* 3	GND
;* 4	SPARE PIN
;* 5	SPARE PIN
;* 6	PORT RC7 I/O
;* 7	PORT RC6 I/O
;* 8	PORT RC5 I/O
;* 9	PORT RC4 I/O
;* 10	PORT RC3 I/O
;* 11	PORT RC2 I/O
;* 12	PORT RC1 I/O
;* 13	PORT RC0 I/O 
;* 14	SPARE PIN
;* 15	SPARE PIN
;* 16	GND
;* 17	PORT RA1(I/O) or AN1(analog input)
;* 18	PORT RA0(I/O) or AN0(analog input)
;*
;*  Switch assignments:(Viewed left to right from the
;*  switch edge of the top of the board ).
;*  Off(up) = logic 1, On(down) = logic 0
;*
;* 8	PORT RB0
;* 7	PORT RB1
;* 6	SPARE SWITCH
;* 5	SPARE SWITCH
;* 4	PORT RB2
;* 3	PORT RB3
;* 2	PORT RB4
;* 1	PORT RB5
;*
;*  Oscillator frequency is about 1.4 MHz using the RC
;*  option with R = 4.7 Kohms and C = 100 pf.
;*  For R = 10 Kohms the osc. freq is 0.8MHz.
;*  That freq. is useful for using PWM for servo motors.
;*  The board includes the pads to, instead, use 
;*  ceramic resonators with intergal capacitors. 4 MHz
;*  and 20 MHz have been successfully tested.
;**********************************************************

	list p=16f876

	; Include file, change directory if needed
	include "p16f876.inc"


	; Start at the reset vector
	org	0x000
	nop			;Required by ICD module
Start
	banksel PORTC		;PORTC is connected to edge connector
	movlw	B'01000001'	;Fosc/8, ch#0, A/D enabled
	movwf	ADCON0		;only ch#0 & #1 are connected to the board edge
 
	banksel OPTION_REG
	movlw	B'00000111'	;Enable port B pullups needed because the switches
				;driving portB are single throw,
	movwf	OPTION_REG	;TMR0 prescaler, 1:256
	clrf	TRISC		;Define PORTC all outputs
	
	;AN2&3 are wired directly to power and ground. Therefore, those pins
	;MUST be defined as Vref+ and Vref-. For this board that means bits
	;3..0 of ADCON1 must have the bit pattern of 1111 or 1101.
	movlw	B'00001111'	;Left justify,1 analog channel
	movwf	ADCON1		;VDD and VSS references

	banksel PORTC

;*  End of SALT 16f876 board description - including some instructions
;*  usually necessary for the operation of that board.
;**********************************************************************************
;*  This program is written to be assembled using MicroChip MPLAB IDE
;*  and downloaden into the SALT 16F876 board using the Microchip
;*  In Circuit Debugger module (ICD).
;*  It may, also, be debugged using the MPLAB Simulator.
;*  Three assembly warnings "Register in operand not in bank 0" are normal.
;**********************************************************************************
;*  Beginning of BLINK program.
;*  Inner loop delay counter - w reg - address 200.
;*  Outer loop delay counter - address 20.
;*Main
;*Turn on light
;* Do outer loop
;*  Do inner loop
;*  Until inner loop done
;* Until outer loop done
;*Turn off light
;* Do outer loop
;*  Do inner loop
;*  Until inner loop done
;* Until outer loop done
;*Go to main
;***********************************************************************************
Main
	bsf	PORTC,0		;turn on output, portc - bit 0.

;**Delay loop 1.
loop1	addlw	0x01		;Increment inner counter.
	btfss	STATUS,2	;Loop until inner counter = 0.
	goto	loop1
	incfsz	0x20,f		;Loop until outer counter = 0.
	goto	loop1	
	
	bcf	PORTC,0		;turn off output, portc - bit 0.

;**Delay loop 2.
loop2	addlw	0x01		;Increment inner counter.
	btfss	STATUS,2	;Loop until inner counter = 0.
	goto	loop2
	incfsz	0x20,f		;Loop until outer counter = 0.
	goto	loop2
		
	goto	Main		;Do it again.

	end