Cypress Semiconductor Perform STK16C88-3 Podręcznik - Strona 4

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Hardware Protect

The

STK16C88-3

offers

inadvertent STORE operation and SRAM WRITEs during low

voltage conditions. When V

initiated STORE operations and SRAM WRITEs are inhibited.

Noise Considerations

The STK16C88-3 is a high speed memory. It must have a high

frequency bypass capacitor of approximately 0.1 µF

connected between V

and V

are as short as possible. As with all high speed CMOS ICs,

careful routing of power, ground, and signals helps prevent

noise problems.

Low Average Active Power

CMOS technology provides the STK16C88-3 the benefit of

drawing significantly less current when it is cycled at times

longer than 50 ns.

Figure 2

relationship between I

Worst case current consumption is shown for both CMOS and

TTL input levels (commercial temperature range, VCC = 5.5V,

100% duty cycle on chip enable). Only standby current is

drawn when the chip is disabled. The overall average current

drawn by the STK16C88-3 depends on the following items:

1. The duty cycle of chip enable

2. The overall cycle rate for accesses

3. The ratio of READs to WRITEs

4. CMOS versus TTL input levels

5. The operating temperature

6. The V

level

7. IO loading

Figure 2. Current Versus Cycle Time (READ)

Document Number: 001-50594 Rev. **

hardware

protection

against

, all externally

CAP

SWITCH

using leads and traces that

SS,

and

Figure 3

shows the

and READ or WRITE cycle time.

Figure 3. Current Versus Cycle Time (WRITE)

Best Practices

nvSRAM products have been used effectively for over 15

years. While ease-of-use is one of the product's main system

values, experience gained working with hundreds of applica-

tions has resulted in the following suggestions as best

practices:

■

The nonvolatile cells in an nvSRAM are programmed on the

test floor during final test and quality assurance. Incoming

inspection routines at customer or contract manufacturer's

sites will sometimes reprogram these values. Final NV

patterns are typically repeating patterns of AA, 55, 00, FF,

A5, or 5A. End product's firmware should not assume a NV

array is in a set programmed state. Routines that check

memory content values to determine first time system config-

uration and cold or warm boot status, should always program

a unique NV pattern (for example, complex 4-byte pattern of

46 E6 49 53 hex or more random bytes) as part of the final

system manufacturing test to ensure these system routines

work consistently.

■

Power up boot firmware routines should rewrite the nvSRAM

into the desired state. While the nvSRAM is shipped in a

preset state, best practice is to again rewrite the nvSRAM

into the desired state as a safeguard against events that

might flip the bit inadvertently (program bugs or incoming

inspection routines).

STK16C88-3

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