
220
Agere Systems Inc.
T8302 Internet Protocol Telephone
Advanced RISC Machine (
ARM
)
Data Sheet
July 2001
16 Parallel Peripheral Interface (PPI)
(continued)
Table 192. PPI Port Sense Register
16.3.3 PPI Port Polarity Register
The
PPI port polarity register
specifies inversion of both input and output signals at general purpose pins. As a
reference, logic signals in the
PPI port data register
are considered to be positive, or active-high. A value of 0 in
the
PPI port polarity register
causes a signal entering or leaving the device on the pin to be inverted, thereby con-
forming to a negative, or active-low signal convention outside the device. Conversely, a value of 1 in the register
causes a signal entering or leaving the device on the pin to be simply buffered, thereby conforming to a positive, or
active-high, signal convention. The interpretation of the register bits differs somewhat for transition-detect inputs, as
described in the following paragraphs.
For an input, a value of 1 in the
PPI port polarity register
results in the value on the input pin being placed in the
PPI port data register
(noninverted, level-sensitive input), while a value of 0 in the
PPI port polarity register
results in the value on the pin being inverted before being placed in the
PPI port data register
(inverted, level-sen-
sitive input).
For a direct-drive output, a 1 in the appropriate bit of the
PPI port polarity register
results in the value in the
PPI port data register
being driven to the chip pin (noninverted, direct drive output), while a 0 in the appropriate bit
of the
PPI port polarity register
results in the inverse of the
PPI port data register
value being driven to the pin
(inverted, direct-drive output).
For an open-drain output, a 1 in the appropriate bit of the
PPI port polarity register
results in the chip pin being
driven to a 0 if there is a 0 in the corresponding
PPI port data register
, and results in the chip pin going to high
impedance if there is a 1 in the
PPI port data register
(non-inverted, open-drain output). For an open-drain output,
a 0 in the appropriate bit of the
PPI port polarity register
results in the chip pin being driven to high impedance if
there is a 0 in the corresponding
PPI port data register
and results in the chip pin being driven to 0 if there is a 1
in the
PPI port data register
(inverted, open-drain output).
On reset, all bits of the
PPI port polarity register
are cleared to 0, indicating inversion.
Table 193. PPI Port Polarity Register
Address 0xE000 600C
Bit #
Name
31:16
RSVD
15:
0
PS[15:
0
]
Bit #
31:16
15:
0
Name
RSVD
PS[15:
0
]
Description
Reserved.
Port sense bits.
If 0, the general purpose output pin is direct-drive. If 1, the
general purpose output pin is open-drain
.
If a PPI bit is an input, the corre-
sponding bit in the PPI port sense register must be set to 0.
Address 0xE000 6010
Bit #
Name
Bit #
31:16
15:
0
31:16
RSVD
15:
0
PP[15:
0
]
Name
RSVD
PP[15:
0
] Polarity bits.
If the bit is set to 1, the corresponding input/output signal is not inverted. If the
bit is set to 0, the corresponding input/output signal is inverted.
Description
Reserved.