DS1305
PIN DESCRIPTIONS (continued)
PIN
FUNCTION
NAME
DIP
TSSOP
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).
12
15
SDI
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 VCCIF 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.
13
14
16
17
SDO
VCCIF
Active-Low Power-Fail Output. The PF pin is used to indicate loss of the
15
16
18
20
PF
primary power supply (VCC1). When VCC1 is less than VCC2 or is less than VBAT,
the PF pin is driven low.
Primary Power Supply. DC power is provided to the device on this pin.
VCC1
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
1Hz
COUNTDOWN CHAIN
4 of 21
DALLAS [ DALLAS SEMICONDUCTOR ]
