DS1384

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TIME-OF-DAY ALARM REGISTERS

Registers 3, 5, and 7 contain the time of day alarm registers. Bits 3, 4, 5, and 6 of register 7 will always

read 0 regardless of how they are written. Bit 7 of registers 3, 5, and 7 are mask bits (Table 1). When all

of the mask bits are logic 0, a time of day alarm will only occur when registers 2, 4, and 6 match the

values stored in registers 3, 5, and 7. An alarm will be generated every day when bit 7 of register 7 is set

to a logic 1. Similarly, an alarm is generated every hour when bit 7 of registers 7 and 5 is set to a logic 1.

When bit 7 of registers 7, 5, and 3 is set to a logic 1, an alarm will occur every minute when register 1

(seconds) rolls from 59 to 00.

Time of day alarm registers are written and read in the same format as the time of day registers. The time

of day alarm flag and interrupt is always cleared when alarm registers are read or written.

WATCHDOG ALARM REGISTERS

Registers C and D contain the time for the Watchdog Alarm. The two registers contain a time count from

00.01 seconds to 99.99 seconds in BCD. The value written into the Watchdog Alarm Registers can be

written or read in any order. Any access to Register C or D will cause the Watchdog Alarm to reinitialize

and clears the Watchdog Flag Bit and the Watchdog Interrupt Output. When a new value is entered or the

Watchdog Registers are read, the Watchdog Timer will start counting down from the entered value to 0.

When 0 is reached, the Watchdog Interrupt Output will go to the active state. The Watchdog Timer

Countdown is interrupted and reinitialized back to the entered value every time either of the registers are

accessed. In this manner, controlled periodic accesses to the Watchdog Timer can prevent the Watchdog

Alarm from ever going to an active level. If access does not occur, countdown alarm will be repetitive.

The Watchdog Alarm Registers always read the entered value. The actual count down register is internal

and is not readable. Writing registers C and D to 0 will disable the Watchdog Alarm feature.

COMMAND REGISTER

Address location 0Bh is the Command Register where mask bits, control bits and flag bits reside. The

operation of each bit is as follows:

Bit 7: TE (Transfer Enable). This bit when set to a logic 0 will disable the transfer of data between

internal and external clock registers. The contents in the external clock registers are now frozen and reads

or writes will not be affected with updates. This bit must be set to a logic 1 to allow updates.

Bit 6: IPSW (Interrupt Switch). When set to a logic 1,

INTA is the Time of Day Alarm and

INTB/(INTB) is the Watchdog Alarm. When set to logic 0, this bit reverses the output pins. INTA is now

the Watchdog Alarm output and

INTB /(INTB) is the Time of Day Alarm output.

applied,

Bit 4: PU/LVL (Interrupt Pulse Mode or Level Mode). This bit determines whether both interrupts

will output a pulse or level signal. When set to a logic 0,

INTA and INTB /(INTB) will be in the level

mode. When this bit is set to a logic 1, the pulse mode is selected and

INTA will sink current for a

minimum of 3 ms and then release.

INTB /(INTB) will either sink or source current, depending on the

condition of bit 5, for a minimum of 3 ms and then release.