C161 Datasheet, PDF (130/400 Pages) Infineon Technologies AG – 16-Bit Single-Chip Microcontroller

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7.2
Output Driver Control
The output driver of a port pin is activated by switching the respective pin to output, i.e.
DPx.y = ’1’. The value that is driven to the pin is determined by the port output latch or
by the associated alternate function (e.g. address, peripheral IO, etc.). The user software
can control the characteristics of the output driver via the following mechanisms:
• Open Drain Mode: The upper (push) transistor is always disabled. Only ’0’ is driven
actively, an external pullup is required.
• Edge Characteristic: The rise/fall time of an output signal can be selected.
Open Drain Mode
In the C161PI certain ports provide Open Drain Control, which allows to switch the output
driver of a port pin from a push/pull configuration to an open drain configuration. In push/
pull mode a port output driver has an upper and a lower transistor, thus it can actively
drive the line either to a high or a low level. In open drain mode the upper transistor is
always switched off, and the output driver can only actively drive the line to a low level.
When writing a ‘1’ to the port latch, the lower transistor is switched off and the output
enters a high-impedance state. The high level must then be provided by an external
pullup device. With this feature, it is possible to connect several port pins together to a
Wired-AND configuration, saving external glue logic and/or additional software overhead
for enabling/disabling output signals.
This feature is controlled through the respective Open Drain Control Registers ODPx
which are provided for each port that has this feature implemented. These registers allow
the individual bit-wise selection of the open drain mode for each port line. If the
respective control bit ODPx.y is ‘0’ (default after reset), the output driver is in the push/
pull mode. If ODPx.y is ‘1’, the open drain configuration is selected. Note that all ODPx
registers are located in the ESFR space.
Figure 7-3 Output Drivers in Push/Pull Mode and in Open Drain Mode
User’s Manual
7-4
1999-08