Any system error (like ?SYNTAX ERROR) will cause output to return to the screen. Devices aren't un-listened by this, so you should send a blank line after an error condition. (See your printer or disk manual for more details.)

   OPEN 4,4: CMD 4,"TITLE" : LIST: REM LISTS PROGRAM ON PRINTER
   PRINT#4: CLOSE 4: REM UN-LISTENS AND CLOSES PRINTER

   10 OPEN 1,1,1,"TEST" : REM CREATE SEQ FILE
   20 CMD 1 : REM OUTPUT TO TAPE FILE, NOT SCREEN
   30 FOR L = 1 TO 100
   40 PRINT L: REM PUTS NUMBER IN TAPE BUFFER
   50 NEXT
   60 PRINT#1 : REM UNLISTEN
   70 CLOSE 1 : REM WRITE UNFINISHED BUFFER, PROPERLY FINISH

CONT

Action: This command re-starts the execution of a program which was halted by a STOP or END statement or the <RUN/STOP> key being pressed. The program will re-start at the exact place from which it left off. While the program is stopped, the user can inspect or change any variables or look at the program. When debugging or examining a program, STOP statements can be placed at strategic locations to allow examination of variables and to check the flow of the program. The error message CAN'T CONTINUE will result from editing the program (even just hitting <RETURN> with the cursor on an unchanged line), or if the program halted due to an error, or if you caused an error before typing CONT to re-start the program.

   10 PI=0:C=1
   20 PI=PI+4/C-4/(C+2)
   30 PRINT PI
   40 C=C+4:GOTO 20