Added files

README.md

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+My experiments with the M68705EVM board
+
+Needs tpasm

test/Makefile

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+PORT=/dev/ttyUSB3
+
+test.srec: test.asm
+	tpasm -P 68705 -o srec test.srec -o text test.txt test.asm
+	@echo "load t"
+	@cat test.srec

test/test.asm

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+;
+;	A0	D4
+;	A1	D5
+;	A2	D6
+;	A3	D7
+;	A4	RS
+;	A5	E
+
+	.ORG 0x80
+
+
+PORTA	.EQU	0x00
+PORTB	.EQU	0x01
+PORTC	.EQU	0x02
+PORTD	.EQU	0x03
+DDRA	.EQU	0x04
+DDRB	.EQU	0x05
+DDRC	.EQU	0x06
+TCR	.EQU	0x08
+TDR	.EQU	0x09
+MR	.EQU	0x0A
+PCR	.EQU	0x0B
+ACR	.EQU	0x0E
+ADR	.EQU	0x0F
+
+SCRATCH	.EQU	0x10
+TMPX	.EQU	0x11
+
+start:
+	JSR	init_dbus
+	JSR	lcd_init
+
+	LDA	#txt_hellorld
+	JSR	print
+
+endloop:
+	BRA	endloop
+
+; Text symbols need to be within the first 255 bytes of the code - cus 8 bit registers.
+txt_hellorld: 
+	DB "Hellorld",0
+
+; Configure port A to be the interface to the LCD
+init_dbus:	
+	LDA	#0xFF			; 0xFF -> A Reg
+	STA	DDRA			; All pins output
+	LDA	#0x00			; 0x00 -> A Reg
+	STA	PORTA			; All pins low
+	RTS
+
+; Send a nibble plus the RS pin
+send_nibble:
+	ORA	#0x20			; Add the E pin high
+	STA	PORTA			; Output the data
+	JSR 	delay			; Wait
+	AND	#0x1F			; Remove the E pin again
+	STA	PORTA			; Output again
+	JSR 	delay			; wait
+	RTS
+
+
+; Send a data byte split into 2 nibbles. Byte is in A
+send_data:
+
+	STA	SCRATCH			; Store the byte for later use
+	.REPEAT 4
+	LSRA				; Shift right 4 times to get the upper nibble
+	.ENDR
+	ORA	#0x10			; Set the RS pin high
+	JSR	send_nibble		; Send it
+
+	LDA	SCRATCH			; Get the old byte back
+	AND	#0x0F			; Mask out just the lower nibble
+	ORA	#0x10			; Add the RS pin again
+	JSR	send_nibble		; Send it
+
+	RTS
+
+; Send an instruction byte split into 2 nibbles. Byte is in A
+send_inst:
+	STA	SCRATCH			; Store the byte for later use
+	.REPEAT 4
+	LSRA				; Shift right 4 times to get the upper nibble
+	.ENDR
+	JSR	send_nibble		; Send it
+
+	LDA	SCRATCH			; Get the old byte back
+	AND	#0x0F			; Mask out the lower nibble
+	JSR	send_nibble		; Send it
+	RTS
+
+
+; Clear the screen and home the cursor
+lcd_clr:
+	LDA	#0x01			; Clear screen instruction
+	JSR	send_inst		; Send it
+	RTS
+
+; Initialize the LCD into 4 bit mode. This assumes that it's in
+; the power-on 8 bit state, otherwise the instructions get out
+; of sequence and things don't work.
+lcd_init:
+	LDA	#0x02			; 4 bit mode
+	JSR	send_nibble
+	LDA	#0x28			; 4 bit mode and 2 line mode
+	JSR	send_inst
+	LDA	#0x0E			; Auto increment
+	JSR	send_inst
+	LDA	#0x06			; Display on
+	JSR	send_inst
+	JSR	lcd_clr			; CLS
+	RTS
+
+; A short delay to make things work.
+delay:
+	STX	TMPX			; Store X into the temporary store
+	LDX	0x13			; 0x13 -> X
+@ldel:
+	NOP				; Nothing
+	DECX				; Decrement X
+	BNE	@ldel			; Repeat until zero
+	LDX	TMPX			; Restore X
+	RTS
+
+; Print a string. Address of the string is in A
+print:
+	TAX				; Put A into X
+@printloop:
+	LDA 	,X			; Grab the byte at X
+	BEQ	@endprint		; If it's zero then bail
+	JSR	send_data		; Send that byte
+	INCX				; Increment X
+	BRA	@printloop		; Next byte.
+
+@endprint:
+	RTS
+
+	
+
+