PULLUP Pin {, Enable}

Function
Enables the internal pull-up resistor for Pin on the SX48 or SX52. This command does not apply to the SX18, SX20, or SX28 (use the PLP_A, PLP_B, and PLP_C registers).

• Pin  is any SX48/52 I/O pin (RA.0 .. RA.7, RB.0 .. RB.7, RC.0 .. RC.7, RD.0 .. RD.7, RE.0 .. RE.7).
• Enable is a constant, 0 or 1, that enables (1) or disables (0) the internal pull-up resistor for Pin. When not specified, Enable defaults to 1.

Explanation
Every I/O pin has an optional internal pull-up resister that can be configured by writing to the appropriate pull-up register (PLP_A, PLP_B, PLP_C, PLP_D and PLP_E). By configuring pull-up resisters on input pins, the SX chip can be connected directly to open/drain circuitry without the need for external pull-up resisters. The internal pull-up resisters are disabled by default. Pull-up resisters can be activated for all pins, regardless of pin direction but really matter only when the associated pin is set to input mode.

Start:
  PULLUP RA.0, 1                                ' enable pull-up
  PULLUP RA.1                                   ' enable pull-up
  PULLUP RA.2, 0                                ' disable pull-up

Related instructions: CMOS, TTL, and SCHMITT