Difference between revisions of "Z80 Routines:Other:DispA"

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[[Category:Z80 Routines:Other|itoa]]
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[[Category:Z80 Routines:Display|DispA]]
[[Category:Z80 Routines|itoa]]
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[[Category:Z80 Routines:Other|DispA]]
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[[Category:Z80 Routines|DispA]]
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Simple and small routines that print the value of z80 register a.
 +
 
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== Decimal Unsigned Version ==
 +
 
 +
<nowiki>;Number in a to decimal ASCII
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;adapted from 16 bit found in z80 Bits to 8 bit by Galandros
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;Example: display a=56 as "056"
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;input: a = number
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;Output: a=0,value of a in the screen
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;destroys af,bc (don't know about hl and de)
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DispA:
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ld c,-100
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call Na1
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ld c,-10
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call Na1
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ld c,-1
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Na1: ld b,'0'-1
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Na2: inc b
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add a,c
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jr c,Na2
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sub c ;works as add 100/10/1
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push af ;safer than ld c,a
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ld a,b ;char is in b
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CALL PUTCHAR ;plot a char. Replace with bcall(_PutC) or similar.
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pop af ;safer than ld a,c
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ret
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</nowiki>
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== Hexadecimal Unsigned Version ==
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<nowiki>;Soon...
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</nowiki>
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== Decimal Signed Version ==
 
  <nowiki>
 
  <nowiki>
; ITOA
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; DispA
 
; --------------------------------------------------------------
 
; --------------------------------------------------------------
 
; Converts a signed integer value to a zero-terminated ASCII
 
; Converts a signed integer value to a zero-terminated ASCII
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; --------------------------------------------------------------
 
; --------------------------------------------------------------
  
itoa:
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DispA:
 
   push    de
 
   push    de
 
   push    bc
 
   push    bc
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     ld    b, 0    ; B will count character length of number
 
     ld    b, 0    ; B will count character length of number
 
-  ld    a, 10
 
-  ld    a, 10
     call  DivHLByA ; HL = HL / A, A = remainder
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     syscall  DivHLByA ; HL = HL / A, A = remainder
 
     push  af
 
     push  af
 
     inc    b
 
     inc    b
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     pop    de
 
     pop    de
 
     ret
 
     ret
 
 
</nowiki>
 
</nowiki>
  
 
===Comments===
 
===Comments===
This routine uses the common radix conversion algorithm of repeatedly dividing a value by the desired radix (base case: the value is zero) and saving the remainders of each division.
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* This routine uses the common [[Wikipedia:Numeral_systems#Change_of_radix|positive-integer radix conversion algorithm]] of repeatedly dividing a value by the desired radix (base case: the value is zero) and saving the remainders of each division.
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* As this algorithm gives the digits in reverse order, they are pushed onto the hardware stack so that subsequently popping them yields the correct order.
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* Note that the output string will not be fixed-width.
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===Example Usage===
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<nowiki>    ld    hl, -1004
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    ld    de, OP1
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    call  DispA
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    ld    hl, OP1
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    syscall  PutS</nowiki>

Latest revision as of 06:51, 21 April 2010


Simple and small routines that print the value of z80 register a.

Decimal Unsigned Version

;Number in a to decimal ASCII
;adapted from 16 bit found in z80 Bits to 8 bit by Galandros
;Example: display a=56 as "056"
;input: a = number
;Output: a=0,value of a in the screen
;destroys af,bc (don't know about hl and de)
DispA:
	ld	c,-100
	call	Na1
	ld	c,-10
	call	Na1
	ld	c,-1
Na1:	ld	b,'0'-1
Na2:	inc	b
	add	a,c
	jr	c,Na2
	sub	c		;works as add 100/10/1
	push af		;safer than ld c,a
	ld	a,b		;char is in b
	CALL	PUTCHAR	;plot a char. Replace with bcall(_PutC) or similar.
	pop af		;safer than ld a,c
	ret

Hexadecimal Unsigned Version

;Soon...

Decimal Signed Version

; DispA
; --------------------------------------------------------------
; Converts a signed integer value to a zero-terminated ASCII
; string representative of that value (using radix 10).
; --------------------------------------------------------------
; INPUTS:
;     HL     Value to convert (two's complement integer).
;     DE     Base address of string destination. (pointer).
; --------------------------------------------------------------
; OUTPUTS:
;     None
; --------------------------------------------------------------
; REGISTERS/MEMORY DESTROYED
; AF HL
; --------------------------------------------------------------

DispA:
   push    de
   push    bc

; Detect sign of HL.
    bit    7, h
    jr     z, _DoConvert

; HL is negative. Output '-' to string and negate HL.
    ld     a, '-'
    ld     (de), a
    inc    de

; Negate HL (using two's complement)
    xor    a
    sub    l
    ld     l, a
    ld     a, 0     ; Note that XOR A or SUB A would disturb CF
    sbc    a, h
    ld     h, a

; Convert HL to digit characters
_DoConvert:
    ld     b, 0     ; B will count character length of number
-   ld     a, 10
    syscall  DivHLByA  ; HL = HL / A, A = remainder
    push   af
    inc    b
    ld     a, h
    or     l
    jr     nz, -

; Retrieve digits from stack
-   pop    af
    or     $30
    ld     (de), a
    inc    de
    djnz   -

; Terminate string with NULL
    xor    a
    ld     (de), a

    pop    bc
    pop    de
    ret

Comments

  • This routine uses the common positive-integer radix conversion algorithm of repeatedly dividing a value by the desired radix (base case: the value is zero) and saving the remainders of each division.
  • As this algorithm gives the digits in reverse order, they are pushed onto the hardware stack so that subsequently popping them yields the correct order.
  • Note that the output string will not be fixed-width.

Example Usage

    ld    hl, -1004
    ld    de, OP1
    call  DispA
    ld    hl, OP1
    syscall  PutS