7-2
Seiko Epson Corporation
S1C31D50 TECHNICAL MANUAL
(Rev. 1.00)
7.2.
I/O Cell Structure and Functions
Figure 7.2.1 shows the I/O cell Configuration.
Figure 7.2.1 I/O Cell Configuration
Refer to
“Pin
Descriptions”
in the
“O
vervie
w”
chapter for the cell type, either the over voltage tolerant
fail-safe type I/O cell or the Bold I/O cell, included in each port.
7.2.1.
Schmitt Input
The input functions are all configured with the Schmitt interface level. When a port is set to input
disable status (PPORTP
x
IOEN.P
x
IEN
y
bit = 0), unnecessary current is not consumed if the P
xy
pin is
placed into floating status.
7.2.2.
Over Voltage Tolerant Fail-Safe Type I/O Cell
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 not consumed when
the port is externally biased without supplying V
DD
. However, be sure to avoid applying a voltage
exceeding the recommended maxi- mum operating power supply voltage to the port.
7.2.3.
Pull-Up/Pull-Down
The GPIO port has a pull-up/pull-down function. Either pull-up or pull-down may be selected for each
port individually. 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 determined by the following equation:
t
PR
= -R
INU
× (C
IN
+ C
BOARD
) × ln(1 - V
T+
/V
DD
)
(Eq. 7.1)
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]
Pull-up/down
control
Analog signal
control
Pull-
up/down
control
Analog signal
control
Pull-up/down
Control signal
Input signal
Input control signal
Output signal
Output control signal
Analog signal
Analog control signal
V
DD
V
DD
V
SS
V
SS
R
INU
/
R
IND
* No diode is
connected at
the VDD
side.
P
xy
Pull-up/down
Control signal
Input signal
Input control signal
Output signal
Output control signal
Analog signal
Analog control signal
V
DD
V
DD
V
SS
V
SS
R
INU
/
R
IND
P
xy
Over voltage tolerant fail-safe type I/O cell
Standard I/O cell
V
DD
V
DD
V
DD
Summary of Contents for S1C31D50
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