Rainbow Electronics DS14287 User Manual

Page 12

DS14285/DS14287

12 of 25

REGISTER C

MSB

LSB

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

IRQF

IRQF - The Interrupt Request Flag (IRQF) bit is set to a 1 when one or more of the following are true:

PF = PIE = 1
AF = AIE = 1
UF = UIE = 1

That is, IRQF = PF

•

=PIE + AF

•

=AIE + UF

•

=UIE.

Any time the IRQF bit is a 1, the

IRQ

pin is driven low. All flag bits are cleared after Register C is read

by the program or when the

RESET

pin is low.

PF - The Periodic Interrupt Flag (PF) is a read-only bit which is set to a 1 when an edge is detected on the
selected tap of the divider chain. The RS3 through RS0 bits establish the periodic rate. PF is set to a 1

independent of the state of the PIE bit. When both PF and PIE are 1s, the

IRQ

signal is active and will set

the IRQF bit. The PF bit is cleared by a

RESET

or a software read of Register C.

AF - A 1 in the Alarm Interrupt Flag (AF) bit indicates that the current time has matched the alarm time.

If the AIE bit is also a 1, the

IRQ

pin will go low and a one will appear in the IRQF bit. A

RESET

or a

read of Register C will clear AF.

UF - The Update Ended Interrupt Flag (UF) bit is set after each update cycle. When the UIE bit is set to

1, the 1 in UF causes the IRQF bit to be a 1 which will assert the

IRQ

pin. UF is cleared by reading

RESET

BIT 0 THROUGH BIT 3 - These are unused bits of the status Register C. These bits always read 0 and
cannot be written.

REGISTER D

MSB LSB

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

VRT

VRT - The Valid RAM and Time (VRT) bit indicates the condition of the internal battery (the battery
connected to the V

BAT

pin in the case of the DS14285S, DS14285, and the DS14285Q). This bit is not

writable and should always be a 1 when read. If a 0 is ever present, an exhausted internal lithium energy
source is indicated and both the contents of the RTC data and RAM data are questionable. This bit is

unaffected by

RESET

BIT 6 THROUGH BIT 0 - The remaining bits of Register D are not usable. They cannot be written and,
when read, they will always read 0.