Hardware manual

Rev. 3.0, 09/98, page 86 of 361
Input Pull-Up Transistors: Port 1 has built-in programmable input pull-up transistors that are
available in modes 2 and 3. The pull-up for each bit can be turned on and off individually. To
turn on an input pull-up in mode 2 or 3, set the corresponding P1PCR bit to “1” and clear the
corresponding P1DDR bit to “0.” P1PCR is cleared to H'00 by a reset and in the hardware standby
mode, turning all input pull-ups off. In software standby mode, the previous state is maintained.
Table 6.4 indicates the states of the input pull-up transistors in each operating mode.
Table 6.4 States of Input Pull-Up Transistors (Port 1)
Mode Reset Hardware Standby Software Standby Other Operating Modes
1 Off Off Off Off
2 Off Off On/off On/off
3 Off Off On/off On/off
Notes: Off: The input pull-up transistor is always off.
On/off: The input pull-up transistor is on if P1PCR = “1” and P1DDR = “0,” but off
otherwise.