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Setting the Time
* RT-TIME SET/DIMMER [Pin 29]
VSS
DIMMER
(1/4 DUTY)
* TIME SET INPUT [Pin 20]
VSS
DOWN
(Back)
(1) Normal operation (current time display mode)
RT-TIME SET/DIMMER pin: Open
TIME SET INPUT pin:
In this state the current time is displayed and inputs to the TIME SET INPUT pin (pin 20) for setting the time will be
ignored.
(2) Current time setting mode
The IC can be switched to the current time setting mode by applying a high level to the RT-TIME SET/DIMMER
pin (pin 29). The current time can only be changed in this mode, and is changed by inputs to the TIME SET INPUT
pin (pin 20). The current time setting mode and the current time display mode can be distinguished by the state of the
colon. If the colon is lit steadily then the IC is in display mode, and if the colon is flashing with a 1 Hz period then
the IC is in setting mode. Normally, the clock continues to operate in setting mode.
If a high level is applied to the TIME SET INPUT pin in setting mode, the second counter is reset to zero and the
time is advanced by one minute. Inversely, if a low level is applied, the second counter is reset to zero and the time is
backed up by one minute. In either case, clock operation is interrupted at the point that the input is applied to the
TIME SET INPUT pin. Furthermore, if the input is held for over 0.5 to 1.0 seconds, the IC switches to quick forward
(or quick reverse) mode. In these modes, counting speed will be 20 msec/count for a 50 Hz input to the 50/60 Hz
INPUT pin, and 17 msec/count for a 60 Hz input to that pin.
When the time has been set, normal clock operation can be restarted by making the TIME SET INPUT pin open.
(3) Dimmer display
RT-TIME SET/DIMMER pin: Low level
If an RC circuit is connected to the CR OSC pin (pin 19) this input can be used to set the LED lit time to 1/4 of that
in normal operation, thus reducing the effective LED brightness. This sets the LED display to a 1/4 duty cycle. In
this mode, the LED on time will 1/4 of that in normal operation, with no influence on any other operation.
If an RC circuit is not provided the LED output will go to zero, i.e., this input can be used to turn off LED display.
This operation is a toggle operation. The first time a low level is applied to the RT-TIME SET/DIMMER pin
dimmed display is setup, and the next time a low level is applied the display will return to normal.
LC85632
OPEN
NOP
(Current time display)
OPEN
NOP
(Current time display)
Open
VDD
Current time setting mode
VDD
UP
(Forward)
No. 4659-20/34
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