DS1689 Datasheet, PDF (4/32 Pages) Dallas Semiconductor – 3-Volt/5-Volt Serialized Real-Time Clock with NV RAM Control

DS1689/DS1693
AD0-AD7 (Multiplexed Bi-directional Address/Data Bus) - Multiplexed buses save pins because
address information and data information time-share the same signal paths. The addresses are present
during the first portion of the bus cycle and the same pins and signal paths are used for data in the second
portion of the cycle. Address/data multiplexing does not slow the access time of the DS1689 since the bus
change from address to data occurs during the internal RAM access time. Addresses must be valid prior
to the latter portion of ALE, at which time the DS1689/DS1693 latches the address. Valid write data must
be present and held stable during the latter portion of the WR pulse. In a read cycle the DS1689/DS1693
outputs 8 bits of data during the latter portion of the RD pulse. The read cycle is terminated and the bus
returns to a high impedance state as RD transitions high. The address/data bus also serves as a bi-
directional data path for the external extended RAM.
ALE (RTC Address Strobe Input; active high) - A pulse on the address strobe pin serves to
demultiplex the bus. The falling edge of ALE causes the RTC address to be latched within the
DS1689/DS1693.
RD (RTC Read Input; active low) - RD identifies the time period when the DS1689/DS1693 drives the
bus with RTC read data. The RD signal is an enable signal for the output buffers of the clock.
WR (RTC Write Input; active low) - The WR signal is an active low signal. The WR signal defines
the time period during which data is written to the addressed register.
CS (RTC Chip Select Input; active low) - The Chip Select signal must be asserted low during a bus
cycle for the RTC portion of the DS1689/DS1693 to be accessed. CS must be kept in the active state
during RD and WR timing. Bus cycles, which take place with ALE asserted but without asserting, CS
will latch addresses. However, no data transfer will occur.
IRQ (Interrupt Request Output; open drain, active low) - The IRQ pin is an active low output of the
DS1689/DS1693 that can be tied to the interrupt input of a processor. The IRQ output remains low as
long as the status bit causing the interrupt is present and the corresponding interrupt-enable bit is set. To
clear the IRQ pin, the application software must clear all enabled flag bits contributing to IRQ ’s active
state.
When no interrupt conditions are present, the IRQ level is in the high impedance state. Multiple
interrupting devices can be connected to an IRQ bus. The IRQ pin is an open drain output and requires an
external pull-up resistor.
CEI (RAM Chip Enable Input; active low) - CEI should be driven low to enable the external RAM.
CEO (RAM Chip Enable Output; active low) - When power is valid, CEO will equal CEI . When
power is not valid, CEO will be driven high regardless of CEI .
PWR (Power-on Output; open drain, active low) - The PWR pin is intended for use as an on/off
control for the system power. With V_CC voltage removed from the DS1689/DS1693, PWR may be
automatically activated from a Kickstart input via the KS pin or from a Wake-up interrupt. Once the
system is powered on, the state of PWR can be controlled via bits in the Dallas registers.
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