6 I/O PORTS (PPORT)
S1C17M20/M21/M22/M23/M24/M25
Seiko Epson Corporation
6-3
TECHNICAL MANUAL (Rev. 1.0)
6.2.1 Schmitt Input
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.
6.2.2 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.
6.2.3 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 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]
6.2.4 CMOS Output and High Impedance State
The I/O cells except for analog output can output signals in the V
DD
and V
SS
levels. Also the GPIO ports may be
put into high-impedance (Hi-Z) state.
6.3 Clock Settings
6.3.1 PPORT Operating Clock
When using the chattering filter for entering external signals to PPORT, the PPORT operating clock CLK_PPORT
must be supplied to PPORT from the clock generator.
The CLK_PPORT supply should be controlled as in the procedure shown below.
1. Enable the clock source in the clock generator if it is stopped (refer to “Clock Generator” in the “Power Supply,
Reset, and Clocks” chapter).
2. Write 0x0096 to the MSCPROT.PROT[15:0] bits. (Remove system protection)
3. Set the following PCLK register bits:
- PCLK.CLKSRC[1:0] bits
(Clock source selection)
- PCLK.CLKDIV[3:0] bits
(Clock division ratio selection = Clock frequency setting)
4. Write a value other than 0x0096 to the MSCPROT.PROT[15:0] bits. (Set system protection)
Settings in Step 3 determine the input sampling time of the chattering filter.