;---------------------------------------------------------------------------
;
;   Programmer  : Larry Aamodt
;
;   File name  	: demo_gpio.s
;   Class       : CPTR-215
;   Language    : ARM assembly
;   Assembler   : Keil
;   Target MCU	: NXP LPC-2148 on Embedded Artists board
;   Date Written: 11/07/12 LDA 
;    change history:  
;    
;   Description	: Example program shows writing to gpio to turn bits on/off
;					 First it loads four addresses into registers
;					 Then programs pins 8 to 15 for output
					 
;   Inputs      :
;   
;   Outputs     : Port zero bits 15 down to bit 8 can be referred to as
;					P0.15 down to P0.8 (ordered as they would be left to
;					right).  Sometimes it seems more natural to refer to
;                   them in counting order, i.e. P0.8 to P0.15
;
;   Special     : This sample code can be run on the simulator.  You 
;  requirements	  can view the gpio pins, see handout.
;   
;
; 	NOTES: 	If this code were run on the hardware board, GPIO bits 8 to 15
;           would turn LEDs on and off.  Also, recall that for a 32 bit word
;           that the left bit is bit 31 and the right bit is bit zero.
;
;---------------------------------------------------------------------------



;  Memory addresses for General Purpose I/O (GPIO) port zero
; IO0PIN	0xE0028000	  This is the actual I/O pin, i.e. the actual I/O
; IO0SET	0xE0028004	  Used to set one or more I/O pins to logic one
; IO0DIR	0xE0028008	  Used to specify signal direction for each pin
; IO0CLR	0xE002800C	  Used to clear one or more I/O pins to logic zero


; User program code goes here
				AREA	demo_gpio, CODE

main            LDR     r1,=0xE0028000  ; load address of I/O port 0 pins
                LDR     r2,=0xE0028004  ; load addr of I/O port 0 set register
				LDR		r3,=0xE0028008	; load addr of I/O port 0 direction reg
                LDR     r4,=0xE002800C  ; load addr of I/O port 0 clear register

                LDR     r0,=0xFF00		; bits 15 down to 8 are ones
                STR     r0,[r3]         ; program pins 15 down to 8 for output

				LDR		r0,=0x0100
				STR     r0,[r2]         ; set pin 8 to logic 1 (high voltage)
				LDR		r5,[r1]			;   read data that is on gpio port zero

				LDR		r0,=0x0200
				STR		r0,[r2]			; set pin 9 to logic 1
				LDR		r6,[r1]			;   read data on gpio port zero

				LDR		r0,=0x0100
				STR		r0,[r4]			; clear pin 8, i.e. make it logic zero
				LDR		r7,[r1]			;   read data on gpio port zero


done            B       done           ; endless loop

; User data area definition follows

                AREA  appdata, DATA, NOINIT, READWRITE

                END