BASIC Month: Terraspin http://reddit.com/r/RetroBattlestations Written by FozzTexx Modified for TRS-80 Model 100 by ChartreuseK Enhanced functions "APSFERK" by ChartreuseK
The file I/O in terraspin-m100-file.bas is written for the TRS-80 Model 100. File I/O should be portable to most BASICs with some form of Disk I/O with a few changes to the syntax. "C$ = INPUT$(1,1)" can be replaced by a function that reads one character from a file. "OPEN FN$ FOR INPUT AS 1" should be replaced by something that opens a file for input "CLOSE 1" should be replaced by something that closes the open file. If your BASIC has a way of rewinding a file then CLOSE+OPEN can be replaced by a rewind. If your BASIC supports random access file I/O. The parts in the ')' and 'R' commands that seek through the file can be replaced by the appropriate command from your BASIC.
|Original commands :---:|--- integer | Push value onto stack ( | Push current IP onto stack (originally intended for loops) ) | Pop BP (val pushed by '(') and a loop counter variable off stack | Decrement loop counter, if < 1 then continue to next byte | else push new loop counter and BP back onto stack, and jump to BP M | Pop V off stack, Move 'turtle' V units in current direction, drawing if pen down T | Pop V off stack, Turn 'turtle' V degrees (ccw) U | Lift pen up (won't draw if moving) D | Place pen down (will draw if moving)
|Added enhanced commands :---:|--- , | Used to seperate two adjacent numbers to push on stack A | Pop top two values on stack, push sum P | Duplicate top value on stack S | Pop top two values on stack, push difference (SK(SP-1) - SK(SP)) F | Swap top two values on stack E | Pop V from stack, Exchange top of stack with value at position SP-V in stack R | Pop V off stack, set IP=V ie. Return, Push IP using ( K | Pop top value off stack C | Call subroutine, pop address off stack, push current IP, jump to address X | Pop top two values on stack, push SK(SP-1) * SK(SP) Q | Pop top two values on stack, push INT(SK(SP-1) / SK(SP))