Rainbow Electronics DS1305 - Manual (Page 3)

DS1305
3 of 20
OPERATION
The block diagram in Figure 1 shows the main elements of the serial alarm RTC. The following
paragraphs describe the function of each pin.
Figure 1. BLOCK DIAGRAM
SIGNAL DESCRIPTIONS
V
CC1
– DC power is provided to the device on this pin. V
CC1
is the primary power supply.
V
CC2
– This is the secondary power supply pin. In systems using the trickle charger, the rechargeable
energy source is connected to this pin.
V
BAT
– Battery input for any standard 3V lithium cell or other energy source. UL recognized to ensure
against reverse charging current when used in conjunction with a lithium battery.
See “Conditions of Acceptability” at http://www.maxim-ic.com/TechSupport/QA/ntrl.htm .
V
CCIF
(Interface Logic Power-Supply Input) – The V
CCIF
pin allows the DS1305 to drive SDO and PF
output pins to a level that is compatible with the interface logic, thus allowing an easy interface to 3V
logic in mixed supply systems. This pin is physically connected to the source connection of the p-channel
transistors in the output buffers of the SDO and
PF pins.
SERMODE (Serial Interface Mode Input) – The SERMODE pin offers the flexibility to choose
between two serial interface modes. When connected to GND, standard 3-wire communication is
selected. When connected to V
CC
, SPI communication is selected.
SCLK (Serial Clock Input) – SCLK is used to synchronize data movement on the serial interface for
either the SPI or 3-wire interface.
1Hz
OSCILLATOR AND
COUNTDOWN CHAIN