DS1305 Datasheet, PDF (4/22 Pages) Dallas Semiconductor – Serial Alarm Real Time Clock RTC

DS1305
PIN DESCRIPTION (continued)
PIN
DIP TSSOP
12
15
13
16
14
17
15
18
NAME
SDI
SDO
V_CCIF
PF
FUNCTION
Serial Data Input. When SPI communication is selected, the SDI pin is the
serial data input for the SPI bus. When 3-wire communication is selected, this
pin must be tied to the SDO pin (the SDI and SDO pins function as a single I/O
pin when tied together).
Serial Data Output. When SPI communication is selected, the SDO pin is the
serial data output for the SPI bus. When 3-wire communication is selected, this
pin must be tied to the SDI pin (the SDI and SDO pins function as a single I/O
pin when tied together).
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.
Active-Low Power-Fail Output. The PF pin is used to indicate loss of the
primary power supply (V_CC1). When V_CC1 is less than V_CC2 or is less than V_BAT,
the PF pin is driven low.
16
20
V_CC1
Primary Power Supply. DC power is provided to the device on this pin.
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
OSCILLATOR AND
COUNTDOWN CHAIN
1Hz
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