I own a TI-99/4A and would like to know if there is an equivalent for POKE in TI BASIC or TI Extended BASIC.
There is no equivalent for POKE or PEEK in standard TI BASIC. This is one example of how TI BASIC differs considerably from other personal computer BASICS. The language designers may have felt that PEEK and POKE commands-which allow programmers to examine and modify individual memory locations-were somehow risky tools to put in the hands of inexperienced programmers. Of course, many inexperienced programmers progress beyond that stage and would find uses for these commands. Constructing a blockade between the programmer and the lower levels of the machine can severely limit a user's control.
Fortunately, TI's Extended BASIC does provide an equivalent for POKE, the CALL LOAD statement. For example, to place the value 100 in location 20000, you'd use CALL LOAD(20000,100). The equivalent to PEEK is CALL PEEK. To place the value from location 20000 into the variable X, you'd use CALL PEEK(200000,X).
Remember that memory for the video display is maintained separately from the microprocessor (and, without expansion, BASIC programs are actually stored in the video memory area), so CALL LOAD and CALL PEEK give you access only to the processor memory or to any attached expansion memory. The ROM in the Mini Memory cartridge also provides for CALL LOAD and CALL PEEK, and in addition provides CALL POKEV and CALL PEEKV, which allow you to store and retrieve data from video memory.
TI also supplies an impressive library of built-in subroutines that accomplish many of the things that PEEK and POKE are used for on other computers. For example, to read the TI joysticks, you can type:
100 CALL JOYST(1,X,Y)
Other valuable features are CALL CHAR, RESEQUENCE, and NUMBER. These provide builtin character redefinition, renumbering, and automatic line-numbering utilities.