STK14C88 View Datasheet(PDF) - Cypress Semiconductor

Part Name

Description

MFG CO.

STK14C88

32Kx8 AutoStore nvSRAM

Cypress Semiconductor 

STK14C88

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 6V should

be provided.

Figure 12. AutoStore Inhibit Mode

In system power mode, both VCC and VCAP are connected to the

+ 5V 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 VCC does not drop below 3.6V during the 10 ms

STORE cycle.

1

32

31

30

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

can be tied to ground and + 5V applied to VCAP (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 VCC should be changed to VCAP throughout this data

sheet. 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

1D6 esi1g7 ns

and those initiated by externally driving HSB low are ignored

unless at least one write operation has taken place since the

w most recent STORE or RECALL cycle. Software initiated STORE

e cycles are performed regardless of whether a write operation has

taken place.

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

r reaches VSWITCH, then a 2.2 ohm resistor should be inserted

fo between VCC and the system supply to avoid momentary excess

of current between Vcc and VCAP.

d Figure 11. AutoStore Mode

e 10k

nd 1

32

e 31

30

omm +

Not Rec 16

17

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 tDELAY; 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 Kohm

resistor to VCAP 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 tDELAY. During tDELAY, multiple

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

when HSB is pulled low it is allowed a time, tDELAY, 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 + 5V is required

because HSB acts as an open drain pull down. The VCAP pins

from the other STK14C88 parts can be tied together and share

a single capacitor. The capacitor size must be scaled by the

AutoStore INHIBIT Mode

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

STK14C88s detects a power loss and asserts HSB, the common

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

can be tied to ground and system power applied to VCAP (Figure

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

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).

function is disabled. If the STK14C88 is operated in this config- During any STORE operation, regardless of how it was initiated,

uration, references to VCC should be changed to VCAP

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

the STK14C88 continues to drive the HSB pin low, releasing it

only when the STORE is complete. Upon completion of the

be triggered through software control. It is not permissible to

STORE operation the STK14C88 remains disabled until the HSB

change between these three options “on the fly.”

pin returns high.

If HSB is not used, leave it unconnected.

Document Number: 001-52038 Rev. *C

Page 12 of 20

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