Rainbow Electronics DDS1693 - Manual (Page 19)

DS1689/DS1693
19 of 32
addition, the other possible interrupt sources within the DS1689/DS1693 may cause IRQ to be driven
low. While system power is applied, the on chip logic will always attempt to drive the PWR pin active in
response to the enabled kickstart or wake-up condition. This is true even if PWR was previously inactive
as the result of power being applied by some means other than wake-up or kickstart.
The system may be powered down under software control by setting the PAB bit to a logic 1. This causes
the open-drain
PWR pin to be placed in a high impedance state, as shown at the beginning of interval 4 in
the timing diagram. As V
CC
voltage decays, the IRQ output pin will be placed in a high impedance state
when V
CC
goes below V
PF
. If the system is to be again powered on in response to a wake-up or kickstart,
then the both the WF and KF flags should be cleared and WIE and/or KSE should be enabled prior to
setting the PAB bit.
During interval 5, the system is fully powered down. Battery backup of the clock calendar and
nonvolatile RAM is in effect,
PWR and IRQ are tri-stated, and monitoring of wake-up and kickstart takes
place.
RAM CLEAR
The DS1689/DS1693 provides a RAM clear function for the 114 bytes of user RAM. When enabled, this
function can be performed regardless of the condition of the V
CC
pin.
The RAM clear function is enabled or disabled via the RAM Clear Enable bit (RCE; bank 1, register
04BH). When this bit is set to a logic 1, the 114 bytes of user RAM will be cleared (all bits set to 1)
when an active low transition is sensed on the
RCLR pin. This action will have no effect on either the
clock/calendar settings or upon the contents of the external extended RAM. The RAM clear Flag (RF,
bank 1, register 04BH) will be set when the RAM clear operation has been completed. If V
CC
is present at
the time of the RAM clear and RIE=1, the IRQ line will also be driven low upon completion. The
interrupt condition can be cleared by writing a 0 to the RF bit. The IRQ line will then return to its inactive
high level provided there are no other pending interrupts. Once the RCLR pin is activated, all read/write
accesses are locked out for a minimum recover time, specified as t
REC
in the Electrical Characteristics
section.
When RCE is cleared to 0, the RAM clear function is disabled. The state of the RCLR pin will have no
effect on the contents of the user RAM, and transitions on the RCLR pin have no effect on RF.
EXTENDED CONTROL REGISTERS
Two extended control registers are provided to supply controls and status information for the extended
features offered by the DS1689/DS1693. These are designated as extended control registers A and B and
are located in register bank 1, locations 04AH and 04BH, respectively. The functions of the bits within
these registers are described as follows.
EXTENDED CONTROL REGISTER 4A
MSB LSB
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
VRT2 INCR * * PAB RF WF KF