TI BASIC

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See How a BASIC program is stored in the computers memory

AND OR

One omission from TI Basic is the lack of logical operators such as AND and OR used for example in expressions such as IF V<8 AND W>4 THEN 120 ELSE 240. TI Basic programmers instead used mathematical operators to replace logical operators.

LIST to a printer

LIST "PIO":130-240 - will LIST to PIO lines 130 to 240 (inclusive)

Reading DATA in a program

For example:

100 FOR A=1 TO 5
110 READ A
120 PRINT A
130 NEXT A
140 DATA 32,45,65,23,4
150 END

It is a peculiarity of the system that when it reaches the last item of data, it takes time out to look to see if there is any more, which can introduce a pause in a long program. A simple solution is to add a couple of dummy DATA items which will never be used, but which will satisfy the computer as to the location of the next data item.

Line 32767

When you have a program with a GOTO or a GOSUB and the line number does not exist - because you have not written it or have deleted it, when you RESequence the program the transfer line will be changed to 32767. eg you will see GOTO 32767 which you never intended.

ODD or EVEN?

Is variable N odd or even?

You might use:

100 X=(N=2*INT(N/2))+1 

which will set X=0 if N is even, and X=1 if N is odd.

Faster:

100 X=N AND 1

Try it.

Check Alpha Lock

A program using the joysticks requires the alpha lock is UP, a relic of the TI99/4 days.

If your program requires the alpha lock to be DOWN for input etc you can instruct the console:

Insert a dummy line CALL KEY(3, Z, Z)

The use of key unit 3 tells the computer to treat the alpha lock as if it were down whilst the program is running, unless we reset. Use of key unit 0 has no effect on alpha lock status. Key unit 5 will reset normal operation.

Month number using POS

Extract a month number, 1 to 12, when the first three letters of any month are entered.

100 INPUT "MONTH?":M$
110 M=(POS("JANFEBMARAPRMAYJ
UNJULAUGSEPOCTNOVDEC",M$,1)+
2)/3
120 IF M<>INT(M) THEN 100
130 PRINT "MONTH NUMBER IS 
";M

Sprites in TI BASIC

You can have sprites if there is a special module inserted such as mini-memory, but this is how to have NO modules inserted and still have 32 sprites in TI Basic. You will need to use cassette files.

This routine allows you to have 32 sprites in TI Basic, with NO modules or peripherals required. The sprites do not have automatic motion, and there is no CALL COINC, but the routine opens up the 32 graphic planes, and allows a character to be placed with single pixel precision. Sprites can be moved manually to give single pixel movement of characters if required.

Now, with no module in place, we do not have POKEV available, so the puzzle is: how, using TI BASIC, can we change memory?

TI Basic has one easy to use command which can change 8 bytes of memory very quickly... it is called CALL CHAR, and it writes these bytes into any area of VDP RAM mapped as 'character definitions'.

VDP Registers shows how by changing VDP Register FIVE, we can move the SPRITE ATTRIBUTE LIST to any part of VDP RAM, INCLUDING the area the console considers to be the character definition table.

If we can do this, then we can use CALL CHAR to write to VDP RAM in an area considered by the CPU to define characters, AND AT THE SAME TIME, define our sprites.

So, the puzzle becomes one of: How do we change the VDP registers using no modules... CALL PEEKV is not available in ordinary TI BASIC.

When you load a program from cassette, there is a HEADER at the start which tells the computer what you are loading and where to put it. Why don't we use the header to place a value into VDP RAM to change the VDP REGISTER!!

NB: If you have more than a cassette recorder, disconnect now! This article is for Console and Cassette ONLY.

The first step is to set the VDP Register, and here is a general register changer ....

Type in this program, then RUN it, with a blank tape in the recorder!

10 REM FILES GENERATOR
20 TO MODIFY VDP REGISTERS
30 REM THANKS IT U.G. BOLOGNA, ITALY
100 CALL CLEAR
110 INPUT "REGISTER # 0-7":R
115 INPUT "VALUE (0-255)":D `
120 A=18429-(256*R+D)
130 X$=CHR$(0)&CHR$(O)&CHRS(0)
14O OPEN #1:"CS1",OUTPUT,FIXED
150 PRINT #1:X$&X$&CHR$(INT(A/256))&CHR$(A)
160 CLOSE #1
170 END

To use the program below, with sprites, you must ENTER the values:

REGISTER=5, VALUE=15

With a value of 15, the sprite table occupies the same memory as the definitions of characters 144 to 159.

If you enter a value of 14, the sprite details are in the same location as characters 128 to 145.

After you have RUN the above program, you will have an odd file on tape.

Do a FULL RESET by typing BYE and reselect TI BASIC. Now LOAD the tape file as though it was a program, with OLD CS1. After you press ENTER at the end of the load, the screen will misbehave (watch for the colour black).

Now press an alphabetic key and then press ENTER. Look .... "MEMORY FULL"!!!

Type in NEW.
The VDP register is now reset until you QUIT or BYE.

Sprites can be placed on the screen as follows:

CALL CHAR(144,"Y1X1F1C1Y2X2F2C2") 
  where Y1, X1 etc are values - 4 values for each sprite)
eg CALL CHAR(144,"04037A0C02057B0B") 
(that is 8 values for TWO sprites, TWO numbers per value)

Where each CALL CHAR carries the four parameters required for two sprites, with each parameter a two digit hexadecimal number.

Y=Row (0-191), X=Column(0-255), F=ASCII+96, C=COLOR(0-15)

What is the HEX for decimal 122?:
122/16= 7 remainder 10 (10=>A where > means HEX)
7/16= 0 remainder 7 ( 7 = >7 )
Therefore 122= >7A

As we are defining two sprites at a time, if you only want one, the final 8 values will be D0000000 to mark the end of the sprite table. If you want two sprites you need to define the next character with a D and 17 zeroes. D0 is the hexadecimal equivalent of 208.

NOTE: As with mini memory, we MUST terminate the sprite table with a value of 208. In other words the final sprite is defined with the values D0000000,

No matter which is the highest value sprite, always end the definition with a hexadecimal equivalent to decimal 208.

The following demo program builds an array H$ such that we can use this to build up the hexadecimal string required.

Ready...
1 REM IT U.G. BOLOGNA ITALY
5 CALL CLEAR
10 DIM(A$(16),H$(255)
20 FOR P=1 TO 15
30 A$(P)=SEG$("0123456789ABCDEF",P+1,1)
35 NEXT P
40 FOR P=0 TO 15
45 K=16*P
50 FOR J=0 TO 15
55 H$(K+J)=A$(P)&A$(J)
50 NEXT J
65 NEXT P
70 REM SPRITE MAGENTA DEMO
75 F$=H$(128)&H$(64+96)
80 F$=F$&H$(14-1)&H$(208)
85 FOR Y=0 TO 191
90 CALL HCHAR(12,12,144)
95 CALL CHAR(144,H$(Y)&F$)
100 NEXT Y
105 GOTO 100