DS1685 Maxim, DS1685 Datasheet - Page 11

• Manufacturer Part Number: DS1685
• Description: The DS1685/DS1687 are real-time clocks (RTCs) designed as successors to the industry-standard DS1285,DS1385, DS1485, and DS1585 PC RTCs
• Manufacturer: Maxim

CONTROL REGISTERS
The four control registers A, B, C, and D reside in both bank 0 and bank 1. These registers are accessible at all
times, even during the update cycle.
Register A (0Ah)
UIP – The update-in-progress (UIP) bit is a status flag that can be monitored. When the UIP bit is a 1, the update
transfer occurs soon. When UIP is a 0, the update transfer does not occur for at least 244s. The time, calendar,
and alarm information in RAM is fully available for access when the UIP bit is 0. The UIP bit is read-only. Writing
the SET bit in Register B to a 1 inhibits any update transfer and clears the UIP status bit.
DV2, DV1, DV0 - These three bits are used to turn the oscillator on or off and to reset the countdown chain. A
pattern of 01X is the only combination of bits that will turn the oscillator on and allow the RTC to keep time. A
pattern of 11X will enable the oscillator but holds the countdown chain in reset. The next update will occur at
500ms after a pattern of 01X is written to DV0, DV1, and DV2. The oscillator enable bit, DV1, will be set to a 1
when V
DV2 = Countdown Chain
DV1 = Oscillator Enable
DV0 = Bank Select
RS3, RS2, RS1, RS0 – These four rate-selection bits select one of the 13 taps on the 15-stage divider or disable
the divider output. The tap selected can be used to generate an output square wave (SQW pin) and/or a periodic
interrupt. The user can do one of the following:
1)
2)
3)
4)
Table 3 lists the periodic interrupt rates and the square-wave frequencies that can be chosen with the RS bits.
Enable the interrupt with the PIE bit;
Enable the SQW output pin with the SQWE or E32K bits;
Enable both at the same time and the same rate; or
Enable neither.
BIT 7
MSB
UIP
1 – resets countdown chain only if DV1=1
0 – countdown chain enabled
1 – oscillator on
0 – oscillator off
1 – extended registers
0 – original bank
CC
is applied.
BIT 6
DV2
BIT 5
DV1
BIT 4
DV0
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BIT 3
RS3
DS1685/DS1687 3V/5V Real-Time Clocks
BIT 2
RS2
BIT 1
RS1
BIT 0
RS0
LSB