Motorola Axiom CMD11E1 Betriebsanweisung PDF herunterladen (Seite 32)

32 CHAPTER 3. FUNCTIONS AND BIT MANIPULATIONS

most often used sentinels are zero (also known as ASCII-Z string), 26 (also known

as CONTROL-Z string, or old DOS string), 4 (EOT string).

The programmers of BUFFALO use EOT string and you have one of two

choices: rewrite BUFFALO routine and use some other sentinel, or use 4 as the

sentinel and remember to place it after each string. The rest of the lab assumes

that you will use the EOT string. Two functions that BUFFALO provides for

printing strings are OUTSTRG at location $FFC7 and OUTSTRGO at location $FFCA.

The diﬀerence between them is that the former will print the string on a new line,

while the latter will continue the string from wherever the cursor happens to be.

Both these functions must be told where the string is. You do this by loading the

X register with the starting address where the string is stored before calling the

function. To enter strings in memory, we use FCC directive. The label associated

with the FCC will be automatically EQUated to the starting address of the string.

Type the following code and verify that OUTSTRG does indeed print a string.

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

OUTSTRG EQU $FFC7

OUTSTRGO EQU $FFCA

; program section. set origin to $C100

ORG $C100

LDX #ABOUTME *STARTING ADDRESS OF THE STRING

JSR OUTSTRG

SWI

; data section. set origin to $D000

ORG $D000

ABOUTME FCC /Hello, my name is ===your name =====/

FCB 4 ;dont forget this

;;;;;;;;;;;;;;;;;;;;;;;end of code ;;;;;;;;;;;;;;;;;;;;;;;;

3.4 Writing your ﬁrst function

Before you write your ﬁrst function, you should observe some standard conven-

tions. Your programs should always start at location $C100, or as speciﬁed by

your TA. Your data should always start at location $D000 or as speciﬁed by your

TA. A small amount of data can be stored starting at location $0000 (Page 0), but

you do not have too much space, 30 bytes or so. It is a matter of taste whether

you write the data section ﬁrst or the program section ﬁrst. You can not mix and

match. I personally prefer the following order: Page 0 section ﬁrst, data section

1 2 ... 27 28 29 30 31 32 33 34 35 36 37 ... 100 101

Keine Kommentare

Motorola Axiom CMD11E1 Betriebsanweisung Seite 32