DS1305
PIN DESCRIPTION
V
CC1
V
CC2
V
BAT
V
CCIF
GND
X1, X2
- Primary Power Supply
- Backup Power Supply
- +3V Battery Input
- Interface Logic Power Supply Input
- Ground
- 32.768 kHz Crystal Connection
INT0
- Interrupt 0 Output
INT1
- Interrupt 1 Output
SDI
- Serial Data In
SDO
- Serial Data Out
CE
- Chip Enable
SCLK
- Serial Clock
SERMODE - Serial Interface Mode
PF
- Power Fail Output
DESCRIPTION
The DS1305 Serial Alarm Real Time Clock provides a full BCD clock calendar which is accessed via a
simple serial interface. The clock/calendar provides seconds, minutes, hours, day, date, month and year
information. The end of the month date is automatically adjusted for months with less than 31 days,
including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with
AM/PM indicator. In addition 96 bytes of nonvolatile RAM are provided for data storage.
An interface logic power supply input pin (V
CCIF
) allows the DS1305 to drive SDO and
PF
pins to a level
that is compatible with the interface logic. This allows an easy interface to 3-volt logic in mixed supply
systems.
The DS1305 offers dual power supplies as well as a battery input pin. The dual power supplies support a
programmable trickle charge circuit which allows a rechargeable energy source (such as a super cap or
rechargeable battery) to be used for a backup supply. The V
BAT
pin allows the device to be backed up by
a non-rechargeable battery. The DS1305 is fully operational from 2.0 to 5.5 volts.
Two programmable time of day alarms are provided by the DS1305. Each alarm can generate an
interrupt on a programmable combination of seconds, minutes, hours and day. “Don’t care” states can be
inserted into one or more fields if it is desired for them to be ignored for the alarm condition. The time of
day alarms can be programmed to assert two different interrupt outputs or to assert one common interrupt
output. Both interrupt outputs operate when the device is powered by V
CC1
, V
CC2
, or V
BAT
.
The DS1305 supports a direct interface to Motorola SPI serial data ports or standard 3-wire interface. A
straightforward address and data format is implemented in which data transfers can occur 1 byte at a time
or in multiple-byte burst mode.
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.
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DALLAS [ DALLAS SEMICONDUCTOR ]
