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60 CHAPTER 5. TABLES

ORG $3000 *data section

...

primes fcb 2,3,5, 7, 11, 13, 17, 19, 23, 29 *table of some primes

nprimes equ 10 *number of entries in the table

If you want to set up a table of ascii code for digits, you would write

...

ORG $3000 *data section

...

digits1 fcb $30, $31, $32, $33, $34, $35, $36, $37, $38, $39

ndigits1 equ 10 *number of entries in the table

A better way to do the same is to write

...

ORG $3000 *data section ..$

...

digits fcc /0123456789/

ndigits equ 10 *number of entries in the table

Assembler will convert FCC to a sequence of FCB.

Exercise: Write an ASM ﬁle with the two versions of the digits tables, assemble

the ﬁle and look at the LST ﬁle. Verify that the two tables are identical.

5.5 Working with tables

We will write functions to perform some basic tasks with the tables. In all these

functions, we will use the following convention:

1. The starting address will be passed to the function in the X register.

2. The size of the table will be passed to the function in the B register.

5.5.1 Table lookup

This is the simplest and the most useful function. We want to know if an element

is in the table. For now, we will work with a table of 8-bit quantities. The value

to be looked up will be passed in the A register. The function will have to return

1 2 ... 55 56 57 58 59 60 61 62 63 64 65 ... 100 101

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Motorola Axiom CMD11E1 Guía de usuario Pagina 60