X-TAL BASIC:
============

The X-tal Basic Interpreter runs under Nas-sys 1 and Nas-sys 3
and needs at least 16K memory starting at 1000h. The
BASIC syntax of this interpreter is very similar to the
syntax of the Nascom ROM Basic made by Microsoft.

X-tal Basic can be expanded by user written assembly programs. 
Informations about that are lost. Here is what we know without
having any original documentation:

Cold Start : E1000
Warm Start : E1002

Commands:
ABS		: absolute value
AND		: logical and
ASC		: get ASCII value if char
ATN		: arcus tangens
CALL p1		: CALL assembly program p1 (address)
CHR$		: get char string of an ASCII value
CLEAR		: 
CLOAD		: cassette load
CMD$		:
CSAVE		: cassette save
CONT		: continue after break
COS		: cosinus
DATA		: data statements
DEF		: define function
DIM		: dim an array
EDIT		: edit a line
END		: end program
ERR		: get error value
EXP		: exp function
FOR		: FOR TO {STEP} NEXT
FN		: function prefix
GOSUB		: call a basic subroutine
GOTO		: goto line
IF		: IF THEN 
INCH		: wait for char from kbd
INPUT		: input a string or value from kbd
INP		: z80 port input
INT		: 
KBD
LEFT$		: left of a string
LET		: variable assignment
LEN		: length of string
LIST		: list program
LOG
MID$
NAS		: return to NAS-SYS
NEXT		: FOR TO NEXT
NEW		: new program (deletes current)
NOT
ON
OR
OUT		: Z-80 port output
PEEK		: peek memory
PI		: 3.141592654
POKE
POP		: pop return address from return stack
POS
PRINT		: print a constant or variable
READ		: read elements from the DATA list
REM		: Remark
RESTORE		
RETURN
RIGHT$
RND
RUN
SIN
SIZE
SGN
SPC(
SPEED
SQR
STEP
STOP
STR$
TAB(
TAN
THEN
TO
VAL$
WAIT