Terminal Functions - Epson RTC-72421 A Applications Manual

RTC - 72421 / 72423

Terminal functions

Signal
RTC-72421 RTC-72423
D -D
0 3
(Data bus)
A -A
0 3
(Address bus)
ALE
(Address Latch Enable)
WR
(WRite)
RD
(ReaD)
CS ,
1
CS
0
(Chip Select)
STD.P
(STanDard Pulse)
V
DD
GND
(V )
DD
N.C.
Pin No. Input/ou
tput
Bi-
11 14 14 16, 19
direction
5, 7, 9, 10 Input
4 7
3 4 Input
10 13 Input
8 11 Input
15,2 20,2 Input
1 1 Output
18 24
9 12
16, 17 22,23
3, 6, 8,
17, 18, 21
Connect these pines to a bi-directional data bus or CPU data bus. Use this bus
to read to and write from the internal counter and registers.
CS CS RD WR
1 0
H L L H
H L H L
H L L L
L H or L
H H H or L
Address input pins used for connection to CPU address, etc. Used to select the
RTC's internal counter and registers (address selection).
When the RTC is connected to a multiplexed-bus type of CPU, these pines can
also be used in combination with the ALE described below
Reads in address data and
CS
When the ALE is high, the address data and
When the (through-mode) ALE falls, the address data and
point are held. The held address data and
the ALE is low.
Address data and CS
ALE
Read into the RTC to set address data
H
Held in the RTC (latched at the trailing edge of the ALE)
L
If the RTC is connected to a CPU that does not have an ALE pin and thus there
is no need to use this ALE pin, fix it to V
Writes the data on D to D into the register of the address specified by A
0 3
A at the leading edge of
3,
WR .
Make sure that and
RD WR
Output data to D to D from the register at the address specified by A
0 3
while is low.
RD
Make sure that and
RD WR
When CS is high and is low, the RTC's chip-select function is valid and
1
CS
0
read and write are enabled.
When the RTC is connected to a multiplexed-bus type of CPU,
the operation of the ALE (see the description of the ALE).
Use CS connected to a power voltage detection circuit. When CS
1
RTC is enabled; when it is low, the RTC is on standby.
When CS goes low, the HOLD and RESET bits in the RTC registers are
1
cleared to 0.
This is an N-channel open drain output pin.
Depending on the setting of the C
pulse signal are output.
The output from this pin cannot be inhibited by the CS
Use a load voltage that is less than or equal to V
open-circuit.
An example of STD.P connection is shown below.
RTC
If the STD.P output is not be used during standby operation, connecting the pull-
up resister to +5 V provides a reduction in current consumption. If the STD.P
output is to be used even during standby, connect the pull-up resistor to the
RTC's V . In this case, the current consumption will be increased by the
DD
amount of current flowing through the pull-up resistor.
Connect this pin to power source. Supply to 5 V
operation; at least 2 V during battery back-up operation.
Connect this pin to ground.
These pins are connected internally to V
These pins are not connected internally. Ground them.
Page - 3
Function
Mode of D D
0 to 3
Output mode (read mode)
Input mode (write mode)
Do not use
High impedance (back-up mode)
High impedance (RTC not selected)
state for internal latching.
0
state is read into the RTC.
CS
0
CS
0
status are maintained while
CS
0
status
0
.
DD
are never low at the same time.
are never low at the same time.
CS
register, a fixed-period interrupt signal and a
E
and
1
CS
0
. If not using this pin, keep it
DD
+5 V or V
DD
At least 2.2 k
STD.P
10 % to this pin during normal
. Leave them open circuit.
DD
MQ - 162 - 03
state at that
0 to
A
0 to 3,
requires
0
is high, the
1
signals.