Epson 0C88832, Technical Manual

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E0C88832/88862 TECHNICAL MANUAL
EPSON
33
5 PERIPHERAL CIRCUITS AND THEIR OPERATION (Input Ports)
5.4 Input Ports (K ports)
5.4.1 Configuration of input ports
The E0C88832/88862 is equipped with 9 input port
bits (K00–K07 and K10) which are usable as general
purpose input port terminals with interrupt
function.
K10 terminal doubles as the external clock (EVIN)
input terminal of the programmable timer (event
counter) with input port functions sharing the
input signal as is. (See "5.10 Programmable Timer")
Each input port is equipped with a pull-up resistor.
The mask option can be used to select either "With
resistor" or "Gate direct" for each input port.
Figure 5.4.1.1 shows the structure of the input port.
Fig. 5.4.1.1 Structure of input port
Each input port terminal is directly connected via a
three-state buffer to the data bus. Furthermore, the
input signal state at the instant of input port
readout is read in that form as data.
5.4.2 Mask option
Input port pull-up resistors
K00 ....
■ ■
With resistor
■ ■
Gate direct
K01 ....
■ ■
With resistor
■ ■
Gate direct
K02 ....
■ ■
With resistor
■ ■
Gate direct
K03 ....
■ ■
With resistor
■ ■
Gate direct
K04 ....
■ ■
With resistor
■ ■
Gate direct
K05 ....
■ ■
With resistor
■ ■
Gate direct
K06 ....
■ ■
With resistor
■ ■
Gate direct
K07 ....
■ ■
With resistor
■ ■
Gate direct
K10 ....
■ ■
With resistor
■ ■
Gate direct
Input ports K00–K07 and K10 are all equipped with
pull-up resistors. The mask option can be used to
select 'With resistor' or 'Gate direct' for each port
(bit).
The 'With resistor' option is rendered suitable for
purposes such as push switch or key matrix input.
When changing the input terminal from LOW level
to HIGH with the built-in pull-up resistor, a delay
in the waveform rise time will occur depending on
the time constant of the pull-up resistor and the
load capacitance of the terminal. It is necessary to
set an appropriate wait time for introduction of an
input port. In particular, special attention should be
paid to key scan for key matrix formation. Make
this wait time the amount of time or more calcu-
lated by the following expression.
Wait time = R
IN
x (C
IN
+ load capacitance on the
board) x 1.6 [sec]
R
IN
: Pull up resistance Max. value
C
IN
: Terminal capacitance Max. value
When 'Gate direct' is selected, the pull-up resistor is
detached and the port is rendered suitable for
purposes such as slide switch input and interfacing
with other LSIs.
In this case, take care that a floating state does not
occur in input.
For unused input ports, select the default setting of
"With resistor".
Input
interrupt
circuit
V
DD
V
SS
Data bus
Kxx
KxxD
Address
Mask
option