Cypress Semiconductor STK14C88-5 Manual do Utilizador descarregar pdf (Página 12)

STK14C88

Document Number: 001-52038 Rev. *D Page 12 of 21

Figure 11 shows the proper connection of capacitors for

automatic store operation. A charge storage capacitor having a

capacity of between 68 µF and 220 µF (±20%) rated at 6 V should

be provided.

In system power mode, both V

and V

CAP

are connected to the

+ 5 V power supply without the 68 µF capacitor. In this mode, the

AutoStore function of the STK14C88 operates on the stored

system charge as power goes down. The user must, however,

guarantee that V

does not drop below 3.6 V during the 10 ms

STORE cycle.

If an automatic STORE on power loss is not required, then V

can be tied to ground and + 5 V applied to V

CAP

(Figure 12). This

is the AutoStore Inhibit mode, in which the AutoStore function is

disabled. If the STK14C88 is operated in this configuration, refer-

ences to V

should be changed to V

CAP

throughout this

datasheet. In this mode, STORE operations may be triggered

through software control or the HSB

pin. To enable or disable

AutoStore using an I/O port pin, see Preventing STORES on

page 13.

To prevent unneeded STORE operations, automatic STOREs

and those initiated by externally driving HSB

low are ignored

unless at least one write operation has taken place since the

most recent STORE or RECALL cycle. Software initiated STORE

cycles are performed regardless of whether a write operation has

taken place.

If the power supply drops faster than 20 ms/volt before V

reaches V

SWITCH

, then a 2.2  resistor should be inserted

between V

and the system supply to avoid momentary excess

of current between V

and V

CAP

Figure 11. AutoStore Mode

AutoStore INHIBIT Mode

If an automatic STORE on power loss is not required, then V

can be tied to ground and system power applied to V

CAP

(Figure 12). This is the AutoStore Inhibit mode, in which the

AutoStore function is disabled. If the STK14C88 is operated in

this configuration, references to V

should be changed to V

CAP

throughout this data sheet. In this mode, STORE operations may

be triggered through software control. It is not permissible to

change between these three options “on the fly.”

Figure 12. AutoStore Inhibit Mode

HSB Operation

The STK14C88 provides the HSB pin for controlling and

acknowledging the STORE operations. The HSB

pin can be used

to request a hardware STORE cycle. When the HSB

pin is driven

low, the STK14C88 conditionally initiates a STORE operation

after t

DELAY

; an actual STORE cycle only begins if a write to the

SRAM took place since the last STORE or RECALL cycle. The

HSB pin has a very resistive pull-up and is internally driven low

to indicate a busy condition when the STORE (initiated by any

means) is in progress. Pull up this pin with an external 10 k

resistor to V

CAP

if HSB is used as a driver.

SRAM read and write operations that are in progress when HSB

is driven low by any means are given time to complete before the

STORE operation is initiated. After HSB

goes low, the STK14C88

continues SRAM operations for t

DELAY

. During t

DELAY

, multiple

SRAM read operations may take place. If a write is in progress

when HSB

is pulled low it is allowed a time, t

DELAY

, to complete.

However, any SRAM write cycles requested after HSB

goes low

are inhibited until HSB

returns high.

The HSB

pin can be used to synchronize multiple STK14C88s

while using a single larger capacitor. To operate in this mode, the

HSB

pin should be connected together to the HSB pins from the

other STK14C88s. An external pull-up resistor to + 5 V is

required because HSB

acts as an open drain pull-down. The

CAP

pins from the other STK14C88 parts can be tied together

and share a single capacitor. The capacitor size must be scaled

by the number of devices connected to it. When any one of the

STK14C88s detects a power loss and asserts HSB

, the common

HSB

pin causes all parts to request a STORE cycle (a STORE

takes place in those STK14C88s that are written since the last

nonvolatile cycle).

During any STORE operation, regardless of how it was initiated,

the STK14C88 continues to drive the HSB

pin low, releasing it

only when the STORE is complete. Upon completion of the

STORE operation the STK14C88 remains disabled until the HSB

pin returns high.

If HSB

is not used, leave it unconnected.



6v, ±20%

0.1



Bypass

10k



10k



Bypass

0.1µF

10K?

Not Recommended for New Designs

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