Rainbow Electronics DS1677 - Manual (Page 4)

DS1677
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X1, X2 – Connections for a standard 32.768 kHz quartz crystal. For greatest accuracy, the DS1677 must
be used with a crystal that has a specified load capacitance of 6 pF. There is no need for external
capacitors or resistors. Note: X1 and X2 are very high impedance nodes. It is recommended that they
and the crystal be guard–ringed with ground and that high frequency signals be kept away from the
crystal area. For more information on crystal selection and crystal layout considerations, please consult
Application Note 58, “Crystal Considerations with Dallas Real Time Clocks”.
The DS1677 will not function without a crystal.
POWER–UP/POWER–DOWN CONSIDERATIONS
When V
CC
is applied to the DS1677 and reaches a level greater than V
CCTP
(power–fail trip point), the
device becomes fully accessible after t
RPU
(250 ms typical). Before t
RPU
elapses, all inputs are disabled.
When V
CC
drops below V
CCSW
, the device is switched over to the V
BAT
supply.
During power–up, when V
CC
returns to an in–tolerance condition, the RST pin is kept in the active state
for 250 ms (typical) to allow the power supply and microprocessor to stabilize.
ADDRESS/COMMAND BYTE
The command byte for the DS1677 is shown in Figure 2. Each data transfer is initiated by a command
byte. Bits 0 through 6 specify the address of the registers to be accessed. The MSB (bit 7) is the
Read/Write bit. This bit specifies whether the accessed byte will be read or written. A read operation is
selected if bit 7 is a zero and a write operation is selected if bit 7 is a one. The address map for the
DS1677 is shown in Figure 3.
ADDRESS/COMMAND BYTE Figure 2
7 6 5 4 3 2 1 0
RD
WR
A6 A5 A4 A3 A2 A1 A0