SAF-C164SM Infineon Technologies, SAF-C164SM Datasheet - Page 138

• Manufacturer Part Number: SAF-C164SM
• Description: 16-Bit CMOS Microcontroller
• Manufacturer: Infineon Technologies

C164CM/C164SM
Derivatives
Parallel Ports
7.1
Output Driver Control
The output driver of a port pin is activated by switching the respective pin to output, that
is, DPx.y = ‘1’. The value 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 pull-up is required.
• Driver Characteristic: The driver strength (delivered current) can be selected.
• Edge Characteristic: The shape of an output signal can be selected.
Open Drain Mode
In the C164CM, certain ports provide Open Drain Control, which allows switching 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 to either a high or a low level. In open drain mode, the upper
transistor is always switched off, and the output driver can actively drive the line to a low
level only. 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 pull-up 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
provided for each port which 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.
External
Pullup
Pin
Pin
Q
Q
Push/Pull Output Driver
Open Drain Output Driver
MCS01975
Figure 7-2
Output Drivers in Push/Pull Mode and in Open Drain Mode
User’s Manual
7-3
V1.0, 2002-02