Motorola Axiom CMD11E1 Guía de usuario descargar pdf (Pagina 35)

3.4. WRITING YOUR FIRST FUNCTION 35

You use FCB to initialize consecutive memory loication (when you transfer the

code from the PC). The label associated with the instruction is needed to deter-

mine the address where the instruction forms the constant. The assembler will

automatically EQUate the label with the address associated with the FCB directive.

Type the following code, assemble it, transfer the S19 ﬁle to the HC11, and

test your program by CALL $C100. Repeat

the CALL statement and verify that

the value in the A changes after each call.

;;;;;;;;;;;;;;;;;;;;;;;start of code ;;;;;;;;;;;;;;;;;;;;;;;;

ORG $C100

JSR RAND

SWI

;;;;;;;;;;;;;;;;;;;;;;;;Start: RAND ;;;;;;;;;;;;;;;;;;

; Function: RAND

; Purpose: Generate a random number

;

; Inputs: None

; Outputs: A random value returned in A registers

;

; Registers modified: A register (which has a random value)

;

; Memory usage: The most recently generated random number is

; stored in memory with label LSTRAND

; This value is used to generate the next value

;

; Notes: Not the best random number generator around but does a

; halfway decent job.

;

; works as follows:

; shift the last random value left and add 20 with carry

;

RAND LDAA SEED

LSLA

In BUFFALO, if you press the enter key at the prompt, BUFFALO will repeat the last

instruction. So you don’t have to type the CALL every time. Just press the enter key.

1 2 ... 30 31 32 33 34 35 36 37 38 39 40 ... 100 101

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Motorola Axiom CMD11E1 Guía de usuario Pagina 35