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Functions built into the Simulator's IO page.
The following table lists the IO functions supported within the IO page. The IO Page is set in the options menu. The variable "IO_AREA" is reserved and will return the start address of the IO page.
IO_AREA+0: TERMINAL_CLS (w)
IO_AREA+1: TERMINAL_OUT (w)
IO_AREA+2: TERMINAL_OUT_CHR (w)
IO_AREA+3: TERMINAL_OUT_HEX (w)
IO_AREA+4: TERMINAL_IN (r)
IO_AREA+5: TERMINAL_X_POS (r/w)
IO_AREA+6: TERMINAL_Y_POS (r/w)
(w) means write only port, (r) read only, (r/w) read/write.
TERMINAL_CLS - clear terminal window, set cursor at (0,0) position.
TERMINAL_OUT - output single character interpreting control characters.
Terminal can only recognize those characters:
ASCII $0D (carriage return) moving cursor to the beginning of line,
ASCII $0A (line feed) moving cursor to the next line and scrolling window if necessary,
ASCII $08 (backspace) moving one position to the left and erasing char below cursor.
TERMINAL_OUT_CHR - outputs single character; control chars are being output just like regular characters.
TERMINAL_OUT_HEX - outputs single byte as a two-digit hexadecimal number.
TERMINAL_IN - input single byte, returns 0 if there's no characters available in terminal's buffer; when I/O terminal window is active it can accept keyboard input; press [Ins] key to paste clipboard's contents into terminal.
TERMINAL_X_POS - cursor X position (column).
TERMINAL_Y_POS - cursor Y position (row).
Use of the Kowalski assembler’s macro language for handling BIOS API and library function calls, the latter which receive parameters via the stack, has helped a lot in that regard—a lot fewer opportunities for minor typos to result in major malfunctions. 
It’s one of the reasons I’m focused on eradicating assembler bugs. 
