Zilog Z08470 Bedienungsanleitung PDF herunterladen (Seite 43)

UM008007-0715 Programming Task Examples

Z80 CPU

User Manual

The program outlined in Table 3 multiplies two unsigned 16-bit integers, leaving the result

in the HL register pair.

Table 3. Multiply Listing

Location

Object

Code Statement Source Statement

0000 1 mult:; unsigned sixteen bit integer multiply.

2 ; on entrance: multiplier in de.

3 ; multiplicand in hl.

5 ; on exit result in hl.

7 ; register uses:

10 ; h high-order partial result

11 ; l low-order partial result

12 ; d high-order multiplicand

13 ; e low-order multiplicand

14 ; b counter for number of shifts

15 ; c high-order bits of multiplier

16 ; a low-order bits of multiplier

17 ;

0000 0610 18 ld b, 16; number of bits-initialize

0002 4a 19 ld c, d; move multiplier

0003 7b 20 ld a, e;

0004 eb 21 ex de, hl; move multiplicand

0005 210000 22 ld hl, 0; clear partial result

0008 cb39 23 mloop: srl c; shift multiplier right

000a if 24 rra least-significant bit is

25 ; in carry.

000b 3001 26 jr nc,

noadd–$;

if no carry, skip the add.

good 19 27 add hl, de; else add multiplicand to

28 ; partial result.

000e eb 29 noadd: ex de, h l; shift multiplicand left

goof 29 30 add hl, hl; by multiplying it by two.

0010 eb 31 ex de, hl;

0011 10f5 32 djnz mloop–$; repeat until no more bits.

0013 c9 33 ret;

34 end;

1 2 ... 38 39 40 41 42 43 44 45 46 47 48 ... 325 326

Keine Kommentare

Zilog Z08470 Bedienungsanleitung Seite 43