AVR turbo pascal strings

The string type introduced by turbo pascal offers too many advantages
to be overlooked. Definition :

array of byte/character with 0th byte as length
up to 255 bytes following

Knowing the length in advance makes it simple to copy them.
A separate length byte allows having the 0x00 being part of the string.
Therefore it is also useable as buffer for communication
Define them as :

.DSEG
mystring	.byte 16	; preset a length including the size

copy string part

; Z^ to Y^, R17 bytes
copystr:
	pushY
	pushZ
cy1:	ld	R16,Z+
	st	Y+,R16
	dec	R17
	brne	cy1
	popZ
	popY
	ret

send string to UART - no IRQ

; sends a string Z^ without the length byte, no interrupt
SendString:
	push	R17
	push	R18
	ld	R17,Z+
ss1:	ld	R18,Z+
	out	UDR,R18
	nop
	nop
ss2:	sbis	USR,UDRE	; wait till out
 	rjmp	ss2
	dec	R17
	brne	ss1
ss3:	sbis	USR,TXC		;wait for last bit out
	rjmp	ss3
	pop	R18
	pop	R17
	ret

append string

; string Z^ gets string X^appended  Z^:=Z^+X^
appendstr:
	pushX
	pushY
	pushZ
	copyZtoY
	push	R17
	push	R18
	push	R19
	push	R20
	ld	R17,Z		;R17:=length(Z)
	mov	R20,R17
	inc	R17
	add	YL,R17		; Y:next after last
	ld	R17,X+		;R17:=length(X)
	mov	R19,R17
	tst	R17
	breq	fienf		; exit if none
fi4:	ld	R18,X+
	st	Y+,R18
	inc	R20
	cpi	R20,LCD_Width
	brne	fi5		;test overlength
	ldi	R17,LCD_Width
	st	Z,R17
	rjmp	fienf
fi5:
	dec	R17
	brne	fi4
;adj size
	ld	R17,Z
	add	R17,R19
	st	Z,R17
fienf:	
	pop	R20
	pop	R19
	pop	R18
	pop	R17
	popZ
	popY
	popX
	ret

byte to hexstring

; byte R17 to hexstring Z^
b2hexstr:
	pushY
	copyZtoY
	push	R18
	push	R19
	ldi	R18,2
	st	Y+,R18
	mov	R18,R17
	andi	R18,0x0F
	ori	R18,0x30
	cpi	R18,0x3A
	brlo	b2hs1
	ldi	R19,7
	add	R18,R19
b2hs1:	st	Y+,R18
	mov	R18,R17
	swap	R18
	andi	R18,0x0F
	ori	R18,0x30
	cpi	R18,0x3A
	brlo	b2hs2
	ldi	U3,7
	add	R18,R19
b2hs2:	st	Y+,R18
	pop	R19
	pop	R18
	popY
	ret

word to hexstring

; word (lsb,msb) R18,R19(msb) to hex string Z^
w2hexstr:
	pushY
	copyZtoY
	push	R20
	push	R21
	ldi	R20,4
	st	Y+,R20
	mov	R20,R19
	swap	R20
	andi	R20,0x0F
	ori	R20,0x30
	cpi	R20,0x3A
	brlo	w2hs1
	ldi	R21,7
	add	R20,R21
w2hs1:	st	Y+,R20
	mov	R20,R19
	andi	R20,0x0F
	ori	R20,0x30
	cpi	R20,0x3A
	brlo	w2hs2
	ldi	R21,7
	add	R20,R21
w2hs2:	st	Y+,R20
	mov	R20,R18
	swap	R20
	andi	R20,0x0F
	ori	R20,0x30
	cpi	R20,0x3A
	brlo	w2hs3
	ldi	R21,7
	add	R20,R21
w2hs3:	st	Y+,R20
	mov	R20,R18
	andi	R20,0x0F
	ori	R20,0x30
	cpi	R20,0x3A
	brlo	w2hs4
	ldi	R21,7
	add	R20,R21
w2hs4:	st	Y+,R20
	pop	R21
	pop	R20
	popY
	ret

notes

the macros used are described here

usage:

	SetZPtr	mystring
	ldi	R17,0x33
	rcall	b2hexstr
	rcall	Sendstring

sends '33' = 0x33 0x33 to the UART



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last updated: 25.dec.99










Copyright (99,2001) Ing.Büro R.Tschaggelar