XC2200 Derivatives
System Units (Vol. 1 of 2)
Parallel Ports
User’s Manual
7-5
V2.1, 2008-08
Parallel Ports, V1.6D6
7.1.2
Input Stage Control
An input stage consists of a Schmitt trigger, which can be enabled or disabled via
software, and an input multiplexer that by default selects the output of the input
Schmitt trigger.
A disabled input driver drives high logical level. During and after reset, all input stages
are enabled by default.
7.1.3
Output Driver Control
An output stage consists of an output driver, output multiplexer, and register bit fields for
their control.
7.1.3.1
Active Mode Behavior
Each output driver can be configured in a push-pull or an open-drain mode, or it can be
deactivated (three-stated). An output multiplexer in front of the output driver selects the
signal source, choosing either the appropriate bit of the Pn_OUT register, or one of
maximum three lines coming from a peripheral unit, see
. The selection is
done via the Pn_IOCR register. Software can set or clear the bit Pn_OUT.Px, which
drives the port pin in case it is selected by the output multiplexer.
An output driver with hardware override can select an additional output signal coming
from a peripheral. While the hardware override is activated, this signal has higher priority
than all other output signals and can not be deselected by the port. In this case, the
peripheral controls the direction of the pin.
7.1.3.2
Power Saving Mode Behavior
In Power Saving Mode (core and IO supply voltages available), the behavior of a pin
depends on the setting of the POCONx.PPSx bit. Basically, groups of four pins within a
port can be configured to react to Power Save Mode Request or to ignore it. In case a
pin group is configured to react to a Power Save Mode Request, each pin within a group
reacts according to its own configuration according to the
7.1.3.3
Reset Behavior
During reset, all output stages of GPIO pins go to tri-state mode without any pull-up or
pull-down device.
7.1.3.4
Power-fail Behavior
When the core supply fails while the pad supply remains stable, the output stages go into
tri-state mode.