I-56
EPSON
S1C88348/317/316/308 TECHNICAL HARDWARE
5 PERIPHERAL CIRCUITS AND THEIR OPERATION (Input Ports)
5.5 Input Ports (K ports)
5.5.1 Configuration of input ports
The S1C88348/317/316 is equipped with 10 input
port bits (K00–K07, K10 and K11) and the S1C88308
is equipped with 9 input port bits (K00–K07, K10)
all of 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 "5.11 Programmable Timer")
Furthermore, it should be noted, however, that K11
terminal (K11 is not available in the S1C88308) is
shared with the bus authority release request signal
(BREQ) input terminal. Function assignment of this
terminal can be selected in software. When this
terminal is selected for BREQ signal, K11 cannot be
used as an input port. (See "5.2 System Controller
and Bus Control")
In the explanation below, it is assumed that K11 is
set as an input port.
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 5.5.1.1 shows the structure of the input port.
Fig. 5.5.1.1 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.
5.5.2 Mask option
Input port pull-up resistors
K00 .... s
s With resistor s
s Gate direct
K01 .... s
s With resistor s
s Gate direct
K02 .... s
s With resistor s
s Gate direct
K03 .... s
s With resistor s
s Gate direct
K04 .... s
s With resistor s
s Gate direct
K05 .... s
s With resistor s
s Gate direct
K06 .... s
s With resistor s
s Gate direct
K07 .... s
s With resistor s
s Gate direct
K10 .... s
s With resistor s
s Gate direct
K11 .... s
s With resistor s
s Gate direct
*
K11 is not available in the S1C88308
Input ports K00–K07, K10 and K11 (K11 is not
available in the S1C88308) 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 = RIN x (CIN + load capacitance on the
board) x 1.6 [sec]
RIN: Pull up resistance Max. value
CIN: 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
VDD
VSS
Data
bus
Kxx
KxxD
Address
Mask
option