Analog Devices ADSP-21261 SHARC Hardware Reference Manual page 530

PBxx_O
PBxx_I
Interface
to SRU
PBENxx_I
Figure 12-5. Pin Buffer Example
The notation for pin input and output connections can be quite confusing
at first because, in a typical system, a pin is simply a wire that connects to
a device. The manner in which pins are connected within the SRU
requires additional nomenclature. The pin interface's input may be
thought of as the input to a buffer amplifier that can drive a load on the
physical external lead. The pin interface enable is the input signal that
enables the output of the buffer by turning it on when its value is logic
high, and turning it off when its value is logic low.
When the pin enable is asserted, the pin output is logically equal to pin
input, and the pin is driven. When the pin enable is deasserted, the output
of the buffer amplifier becomes high impedance. In this situation, an
external device may drive a level onto the line, and the pin is used as an
input to the ADSP-2126x processor.
12-8
PIN
IN
OUT
BUFFER
ENABLE
ADSP-2126x SHARC Processor Hardware Reference
External
PBxx_O
Package
Connection
Pin