DS1254 Maxim, DS1254 Datasheet - Page 6

• Manufacturer Part Number: DS1254
• Description: The DS1254 is a fully nonvolatile static RAM (NV SRAM) (organized as 2M words by 8 bits) with built-in real-time clock
• Manufacturer: Maxim

DS1254
AM/PM/12/24 MODE
Bit 7 of the hours register is defined as the 12-hour or 24-hour mode select bit. When high, the 12-hour mode is
selected. In the 12-hour mode, bit 5 is the AM/PM bit with logic high being PM. In the 24-hour mode, bit 5 is the
second 10-hour bit (20–23 hours).
OSCILLATOR BIT
Bit 5 of the day register controls the oscillator. When set to logic 1, the oscillator is off. When set to logic 0, the
oscillator turns on and the watch becomes operational.
ZERO BITS
Registers 1, 2, 3, 4, 5, and 6 contain one or more bits that will always read logic 0. When writing these locations,
either a logic 1 or logic 0 is acceptable.
BATTERY MONITORING
The DS1254 automatically monitors the battery in an attached DS3800 battery cap on a 24-hour time interval. Such
monitoring begins within t
after V
rises above V
and is suspended when power failure occurs.
REC
CC
PF
After each 24-hour period has elapsed, the battery is connected to an internal 1M test resistor for one second.
During this one second, if the battery voltage falls below the battery-voltage trip point (~2.6V), the battery warning
output BW is asserted. Once asserted, BW remains active until the attached DS3800 battery cap is replaced.
However, the battery is still retested after each V
power-up, even if it was active on power-down. If the battery
CC
voltage is found to be higher than ~2.6V during such testing, BW is de-asserted and regular testing resumes. BW
has an open-drain output driver.
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