Cypress Semiconductor Perform nvSRAM Dokumentacja Pobierz pdf (Strona 9)

CY14B256KA

Document Number: 001-55720 Rev. *H Page 9 of 28

interrupt on INT pin is also generated on watchdog timeout. The

flag and the hardware interrupt are both cleared when user reads

the flags register.

Power Monitor

The CY14B256KA provides a power management scheme with

power fail interrupt capability. It also controls the internal switch

to backup power for the clock and protects the memory from low

access. The power monitor is based on an internal band gap

reference circuit that compares the V

voltage to V

SWITCH

threshold.

As described in the AutoStore Operation on page 4, when

SWITCH

is reached as V

decays from power loss, a data

STORE operation is initiated from SRAM to the nonvolatile

elements, securing the last SRAM data state. Power is also

switched from V

to the backup supply (battery or capacitor) to

operate the RTC oscillator.

When operating from the backup source, read and write

operations to nvSRAM are inhibited and the RTC functions are

not available to the user. The RTC clock continues to operate in

the background. The updated RTC time keeping registers data

are available to the user after V

is restored to the device (see

AutoStore/Power-Up RECALL on page 21).

Interrupts

The CY14B256KA has flags register, interrupt register and

interrupt logic that can signal interrupt to the microcontroller.

There are three potential sources for interrupt: watchdog timer,

power monitor, and alarm timer. Each of these can be individually

enabled to drive the INT pin by appropriate setting in the interrupt

the flags register (0x7FF0) that the host processor uses to

determine the cause of the interrupt. The INT pin driver has two

bits that specify its behavior when an interrupt occurs.

An interrupt is raised only if both a flag is raised by one of the

three sources and the respective interrupt enable bit in interrupts

two programmable bits, H/L and P/L, determine the behavior of

the output pin driver on INT pin. These two bits are located in the

interrupt register and can be used to drive level or pulse mode

output from the INT pin. In pulse mode, the pulse width is

internally fixed at approximately 200 ms. This mode is intended

to reset a host microcontroller. In the level mode, the pin goes to

its active polarity until the flags register is read by the user. This

mode is used as an interrupt to a host microcontroller. The

control bits are summarized in the following section.

Interrupts are only generated while working on normal power and

are not triggered when system is running in backup power mode.

Note CY14B256KA generates valid interrupts only after the

Powerup RECALL sequence is completed. All events on INT pin

must be ignored for t

HRECALL

duration after powerup.

Interrupt Register

Watchdog Interrupt Enable (WIE). When set to ‘1’, the

watchdog timer drives the INT pin and an internal flag when a

watchdog time out occurs. When WIE is set to ‘0’, the watchdog

timer only affects the WDF flag in flags register.

Alarm Interrupt Enable (AIE). When set to ‘1’, the alarm match

drives the INT pin and an internal flag. When AIE is set to ‘0’, the

alarm match only affects the AF flag in flags register.

Power Fail Interrupt Enable (PFE). When set to ‘1’, the power

fail monitor drives the pin and an internal flag. When PFE is set

to ‘0’, the power fail monitor only affects the PF flag in flags

High/Low (H/L). When set to a ‘1’, the INT pin is active HIGH

and the driver mode is push pull. The INT pin drives high only

when V

is greater than V

SWITCH

. When set to a ‘0’, the INT pin

is active LOW and the drive mode is open drain. The INT pin

must be pulled up to Vcc by a 10 k resistor while using the

interrupt in active LOW mode.

Pulse/Level (P/L). When set to a ‘1’ and an interrupt occurs, the

INT pin is driven for approximately 200 ms. When P/L is set to a

‘0’, the INT pin is driven high or low (determined by H/L) until the

flags register is read.

When an enabled interrupt source activates the INT pin, an

external host reads the flags register to determine the cause. All

flags are cleared when the register is read. If the INT pin is

programmed for level mode, then the condition clears and the

INT pin returns to its inactive state. If the pin is programmed for

pulse mode, then reading the flag also clears the flag and the pin.

The pulse does not complete its specified duration if the flags

flags register is not read during a reset.

Flags Register

The flags register has three flag bits: WDF, AF, and PF, which

can be used to generate an interrupt. These flags are set by the

watchdog timeout, alarm match, or power fail monitor

respectively. The processor can either poll this register or enable

interrupts to be informed when a flag is set. These flags are

automatically reset when the register is read. The flags register

is automatically loaded with the value 0x00 on power-up (except

for the OSCF bit; see Stopping and Starting the Oscillator on

page 7).

Figure 3. Watchdog Timer Block Diagram

1 Hz

Oscillator

Clock

Divider

Counter

Zero

Compare

WDF

WDS

Load

WDW

Watchdog

write to

Watchdog

32 Hz

32,768 KHz

1 2 3 4 5 6 7 8 9 10 11 12 13 14 ... 27 28

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