Timing Waveforms

Read Timing Diagram

TLF9981 – 3

Write Timing Diagram

TLF9981 – 4

Pin Description

CS RD WR (Inputs)

These pins interface to mP control

lines The CS pin is an active low enable for the read and

write operations Read and Write pins are also active low

and enable reading or writing to the RTC All three pins are

disabled when power failure is detected However if a read

or write is in progress at this time it will be allowed to com-

plete its cycle

A0 – A4 (Inputs)

These 5 pins are for register selection

They individually control which location is to be accessed

These inputs are disabled when power failure is detected

OSC IN (Input) OSC OUT (Output)

These two pins are

used to connect the crystal to the internal parallel resonant

oscillator The oscillator is always running when power is

MFO (Output)

The multi-function output can be used as a

second interrupt (Power fail) output for interrupting the mP

This pin can also provide an output for the oscillator The

MFO output is configured as push-pull active high for nor-

mal or single power supply operation and as an open drain

mode and a pull-up resistor is attached it should be con-

INTR (Output)

The interrupt output is used to interrupt the

processor when a timing event or power fail has occurred

and the respective interrupt has been enabled The INTR

output is permanently configured active low open drain If in

battery backed mode and a pull-up resistor is attached it

output is a DC voltage level To clear the INTR writea1to

the appropriate bit(s) in the Main Status Register

D0 – D7 (InputOutput)

These 8 bidirectional pins connect

to the host mP’s data bus and are used to read from and

write to the RTC When the PFAIL pin goes low and a write

is not in progress these pins are at TRI-STATE

PFAIL (Input)

In battery backed mode this pin can have a

digital signal applied to it via some external power detection

mode in a minimum of 30 ms or a maximum of 63 ms unless

lockout delay is programmed In the single power supply

mode this pin is not useable as an input and should be tied

tion

up power supply This power supply is switched to the inter-

ing this pin eliminates the need for external logic to switch in

and out the back-up power supply If this feature is not to be

used then this pin must be tied to ground the RTC pro-

grammed for single power supply only and power applied to

GND

4