LOOKDOWN Target, Value0, {Value1, Value2, ...} Variable

Function
Compare Target value to a list of values and store the index number of the first value that matches into ByteVar. If no value in the list matches, Variable is left unaffected.

• Target  is a byte variable or constant (0 - 255) to be compared to the values in the list.
• Values  are byte variables or constants (0 - 255) to be compared to Target.
• Variable  is a byte or word variable that will be set to the index (0 - n) of the matching value in the Values list. If no matching value is found, Variable is left unaffected.

Explanation
LOOKDOWN works like the index in a book. In an index, you search for a topic and get the page number. LOOKDOWN searches for a target value in a list, and stores the index number of the first match in a variable. For example:

Do_Cmd:
  DO
    SERIN Sio, Baud, cmd                        ' wait for command input
    LOOKDOWN cmd, "F", "B", "S", cmd            ' compare against valid commands
  LOOP UNTIL cmd < 3                            ' wait until valid
  BRANCH cmd, Forward, Backward, Stop_Bot       ' execute valid command

Related instruction: LOOKUP