Programming for Microprocessors

82

Some programming techniques

SUBROUTINE AA: entered with the base address of an array

(i.e.

the address of the first element) in the index register, and the

relative position of a selected element in accumulator

B;

the sub-

routine calculates the absolute address of the selected element

and delivers it in the index register.

As a final illustration we shall discuss the problem of generating a

two-digit decimal display. The definition of such a subroutine has

already been given on page 72. The program assumes that two seven-

segment displays are connected to the address bus at location ?F100

-

9

f

e

d

c

b

α

Figure 7.2

and

?F101 .

Each displa