Cypress STK16C88 - Manual (Page 4)

STK16C88
Document Number: 001-50595 Rev. ** Page 4 of 14
Hardware Protect
The STK16C88 offers hardware protection against inadvertent
STORE operation and SRAM WRITEs during low voltage
conditions. When V
CAP
<V
SWITCH
, all externally initiated
STORE operations and SRAM WRITEs are inhibited.
Noise Considerations
The STK16C88 is a high speed memory. It must have a high
frequency bypass capacitor of approximately 0.1 µF
connected between V
CC
and V
SS,
using leads and traces that
are as short as possible. As with all high speed CMOS ICs,
careful routing of power, ground, and signals reduce circuit
noise.
Low Average Active Power
CMOS technology provides the STK16C88 the benefit of
drawing significantly less current when it is cycled at times
longer than 50 ns.
Figure 2 and Figure 3 shows the
relationship between I
CC
and READ or WRITE cycle time.
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 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
CC
level
7. IO loading
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, 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 an NV array is in
a set programmed state. Routines that check memory
content values to determine first time system configuration
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).
Figure 2. Current Versus Cycle Time (READ)
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