Difference between revisions of "Programming:Display a 8-bit number in hex"
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| + | From the '''The Unofficial Amstrad WWW Resource''': | ||
| + | |||
| + | This routine uses [[Firmware]] | ||
| + | |||
<pre> | <pre> | ||
;; A procedure to display a 8-bit number in hex form | ;; A procedure to display a 8-bit number in hex form | ||
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jp txt_output ;display digit | jp txt_output ;display digit | ||
</pre> | </pre> | ||
| + | |||
| + | The .print_byte_digit routine can be further optimised by devious use of DAA | ||
| + | |||
| + | <pre> | ||
| + | ;;------------------------------------------- | ||
| + | ;; display number in lower nibble (bits 3..0) | ||
| + | .print_byte_digit | ||
| + | and %00001111 ;isolate lower nibble. (This contains the digit value 0...15) | ||
| + | cp &a ;Less than 10? Set carry if so | ||
| + | sbc a,&69 | ||
| + | daa ;Because previous instruction was a subtract operation this | ||
| + | ;is known as 'das' in x86 | ||
| + | jp txt_output ;display digit | ||
| + | </pre> | ||
| + | |||
| + | [[Category:Programming]] | ||
Latest revision as of 10:24, 20 January 2015
From the The Unofficial Amstrad WWW Resource:
This routine uses Firmware
;; A procedure to display a 8-bit number in hex form
;;
.txt_output equ &bb5a
;;----------------------------
;; DISPLAY A BYTE IN HEX FORM
;;
;; Enter:
;; A = 8-bit value
;;
;; Exit:
;; AF corrupt, All other registers preserved
.print_hex_byte
push af ;store original byte value
;; move upper nibble into lower nibble
rrca
rrca
rrca
rrca
;; display nibble as ASCII
call print_byte_digit
pop af ;retrieve original byte value
;;-------------------------------------------
;; display number in lower nibble (bits 3..0)
.print_byte_digit
and %00001111 ;isolate lower nibble. (This contains the digit value 0...15)
add a,"0" ;add ASCII for 0. Digits 0...9 become "0"..."9", digits 10..15
;become ":"...."A"
cp "9"+1
jr c,number ;if number is in digit range 0...9, display digit
add a,"A"-"9"-1 ;modify ASCII value so that digits in the range 10...15
;;become "A"...."F"
.number
jp txt_output ;display digit
The .print_byte_digit routine can be further optimised by devious use of DAA
;;-------------------------------------------
;; display number in lower nibble (bits 3..0)
.print_byte_digit
and %00001111 ;isolate lower nibble. (This contains the digit value 0...15)
cp &a ;Less than 10? Set carry if so
sbc a,&69
daa ;Because previous instruction was a subtract operation this
;is known as 'das' in x86
jp txt_output ;display digit
