TI BASIC (TI 99/4A) Totally Explained

Everything about Ti Basic Ti 99 4a totally explained

ť This article is about the TI-99/4A Home Computer programming language. For the calculator language, see TI-BASIC (calculators) (note: hyphen between "TI" and "BASIC" in that one).TI BASIC was a dialect of BASIC for the Texas Instruments TI-99/4A Home Computer (1981), developed under contract to Microsoft by Bob Wallace and Bob Greenberg. A version supporting compiled code was also used as a commercial development language for the TI-990 range of minicomputers.

TI BASIC was built into the 99/4 and 99/4A, and was remarkably easy to learn. Users could access functions through this simple language that on other computers would only be available to those versed in the machines' assembly language code. Text, full screen graphics, logic operations, and recording to tape (or any other file system - diskettes, RS-232 interface, RAM disks) could all be accomplished using TI BASIC. TI also produced an Extended BASIC cartridge that greatly enhanced the functionality accessible to BASIC users.

Elements of TI BASIC

Statements

The statements of TI BASIC are CALL, CLOSE, DATA, DEF, DIM, END, FOR..TO..STEP, GOSUB, GOTO, IF..THEN..ELSE, INPUT, LET, NEXT, ON..GOSUB, ON..GOTO, OPEN, OPTION BASE, PRINT, RANDOMIZE, READ, REM, RESTORE, RETURN, STOP
Every line of TI BASIC can only contain one statement. The possibility to put several statements in a line with :: became available in TI Extended BASIC and the necessary PEEK and LOAD calls to use assembly language routines. Note that there's no POKE statement in TI BASIC. Loading and executing machine code requires a 32K memory expansion and the TI Editor/Assembler cartridge, which then gives access CALL LOAD. The 256 Bytes of RAM directly accessible by the CPU was mostly consumed by the BASIC interpreter. TI BASIC stored and ran programs from the 16K video RAM, and, unlike TI Extended BASIC, couldn't take advantage of the 32K memory expansion.

Functions

ABS Absolute value
ASC ASCII numeric value of the first character of a string
ATN Arctangent
CHR$ Convert a number into a string with an ASCII character
COS Cosine
EOF Test whether the end of a file has been reached
EXP Exponentiation
INT greatest integer less than or equal to the parameter
LEN Length of a string
LOG Natural logarithm
POS First occurrence of a string in another string
RND Pseudorandom number generator
SEG$ Return a substring of a string
SGN Sign function
SIN Sine
SQR Square root
STR$ Convert a number to a string
TAN Tangent
VAL Convert a string to a number

Subprograms

Subprograms are called with CALL statement (for example CALL CLEAR). There are no user defined subprograms (This is possible in TI Extended BASIC), but some subprograms are predefined:

CHAR Definition of graphical characters

CLEAR Clears the screen

COLOR Defines foreground- and background color for 8 characters

GCHAR Reads one character at a specified position from the screen

HCHAR Writes a character to a screen position and repeats it horizontally

JOYST Returns the position of the joystick

KEY Reads from the keyboard without echo on the screen

SCREEN Changes the color of the screen

SOUND Creates sounds (using a frequency) and noise

VCHAR Writes a character to a screen position and repeats it vertically

Execution speed

One serious shortcoming of TI BASIC was that, as an interpreted rather than compiled language, it was inherently slow. TI BASIC was a double interpreted language, as the BASIC interpreter was itself written in a mid-layer interpreted byte-code language known as Graphics Programming Language (GPL), which was unique to the TI Home Computer. TI Extended BASIC improved execution speed somewhat by providing some functionality in assembly language.

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