6 I/O PORTS (PPORT)
6-2
Seiko epson Corporation
S1C17F13 TeChniCal Manual
(Rev. 1.0)
I/O Cell Structure and Functions
6.2
Figure 6.2.1 shows the I/O cell Configuration.
Pull-up/down
Control signal
Over voltage tolerant fail-safe type I/O cell
Input signal
Input control signal
Output signal
Output control signal
Analog signal
Analog control signal
Pull-up/down
Control signal
Input signal
Input control signal
Output signal
Output control signal
Analog signal
Analog control signal
Pull-up/down
control
Analog signal
control
V
DD
V
DD
V
DD
V
SS
P
xy
V
SS
Standard I/O cell
Pull-up/down
control
Analog signal
control
V
DD
V
DD
V
DD
V
DD
V
SS
P
xy
V
SS
∗
No diode is
connected at
the V
DD
side.
R
INU
/
R
IND
R
INU
/
R
IND
2.1 I/O Cell Configuration
Figure 6.
Refer to “Pin Descriptions” in the “Overview” chapter for the cell type, either the over voltage tolerant fail-safe
type I/O cell or the standard I/O cell, included in each port.
Schmitt Input
6.2.1
The input functions are all configured with the Schmitt interface level. When a port is set to input disable status
(P
x
IOEN.P
x
IEN
y
bit = 0), unnecessary current is not consumed if the P
xy
pin is placed into floating status.
Over Voltage Tolerant Fail-Safe Type I/O Cell
6.2.2
The over voltage tolerant fail-safe type I/O cell allows interfacing without passing unnecessary current even if a
voltage exceeding V
DD
is applied to the port. Also unnecessary current is consumed when the port is externally bi-
ased without supplying V
DD
. However, be sure to avoid applying a voltage exceeding the recommended maximum
operating power supply voltage to the port.
Pull-Up/Pull-Down
6.2.3
The GPIO port has a pull-up/pull-down function. Either pull-up or pull-down may be selected for each port indi-
vidually. This function may also be disabled for the port that does not require pulling up/down.
When the port level is switched from low to high through the pull-up resistor included in the I/O cell or from high
to low through the pull-down resistor, a delay will occur in the waveform rising/falling edge depending on the time
constant by the pull-up/pull-down resistance and the pin load capacitance. The rising/falling time is commonly de-
termined by the following equation:
t
PR
= -R
INU
×
(C
IN
+ C
BOARD
)
×
ln(1 - V
T+
/V
DD
)
(Eq. 6.1)
t
PF
= -R
IND
×
(C
IN
+ C
BOARD
)
×
ln(1 - V
T-
/V
DD
)
Where
t
PR
:
Rising time (port level = low
→
high) [second]
t
PF
:
Falling time (port level = high
→
low) [second]
V
T+
:
High level Schmitt input threshold voltage [V]
V
T-
:
Low level Schmitt input threshold voltage [V]
R
INU
/R
IND
: Pull-up/pull-down resistance [
W
]
C
IN
:
Pin capacitance [F]
C
BOARD
: Parasitic capacitance on the board [F]