9.6.4 Built-In MOS Pull-Up
The MOS input pull-ups of port 5 are turned on by clearing the corresponding bit in P5DDR to
“0” and writing a “1” in P5DR. These pull-ups are turned off at a reset and in the hardware
standby mode. Table 9-9 indicates the status of the MOS pull-ups in various modes.
Table 9-9 Status of MOS Pull-Ups for Port 5
Mode Reset Hardware Standby Mode Other Operating States*
1 OFF OFF OFF
2 ON/OFF
3 OFF
4
7
* Including the software standby mode.
Notation:
OFF: The MOS pull-up is always off.
ON/OFF: The MOS pull-up is on when P5DDR = 0 and P5DR = 1, and off otherwise.
Note on Usage of MOS Pull-Ups
If the bit manipulation instructions listed below are executed on input/output ports 5 and 6 which
have selectable MOS pull-ups, the logic levels at input pins will be transferred to the DR latches,
causing the MOS pull-ups to be unintentionally switched on or off.
This can occur with the following bit manipulation instructions: BSET, BCLR, BNOT
(1) Specific Example (BSET Instruction): An example will be shown in which the BSET
instruction is executed for port 5 under the following conditions:
P57: Input pin, low, MOS pull-up transistor on
P56: Input pin, high, MOS pull-up transistor off
P55 – P50: Output pins, low
The intended purpose of this BSET instruction is to switch the output level at P50 from low
to high.
ON/OFF
161
Downloaded from Elcodis.com electronic components distributor
To Next Page
Loading...
