NSAM266SA Datasheet, PDF (8/52 Pages) National Semiconductor (TI) – NSAM266SA CompactSPEECHTM Digital Speech Processor with Serial Flash Interface

1 0 Hardware (Continued)
1 3 3 Power-Down Mode
Power-down mode is useful during a power failure when the
power source for the CompactSPEECH is a backup battery
or in battery powered devices while the CompactSPEECH
is idle
In power-down mode the clock frequency of the Compact-
SPEECH is reduced and some of the processor modules
are deactivated As a result the CompactSPEECH con-
sumes much less power than in normal-power mode
(^k 1 5 mA) Although the CompactSPEECH does not per-
form all its usual functions in power-down mode it still
keeps stored messages and maintains the time of day
Note In power-down mode all the chip select signals CS0 to CS3 are set
to 1 To guarantee that there is no current flow from these signals to
the Serial Flash devices the power supply to these devices must not
be disconnected
The CompactSPEECH stores messages and all memory
management information in flash memory Thus there is no
need to maintain the power to the processor to preserve
stored messages If the microcontroller’s real-time clock
(and not the CompactSPEECH’s real-time clock) is used to
maintain the time and day neither the flash nor the
CompactSPEECH require battery backup during power fail-
ure In this case when returning to normal mode the micro-
controller should perform the initialization sequence as de-
scribed in Section 2 10 and use the SETD command to set
the time and day
To keep power consumption low in power-down mode the
RESET MWCS MWCLK and MWDIN signals should be
held above V_CC b 0 5V or below V_SS a 0 5V
The PDM (Go To Power-down Mode) command switches
the CompactSPEECH to power-down mode (For an expla-
nation of the CompactSPEECH commands see Section
2 14 ) It may only be issued when the CompactSPEECH is
in the IDLE state (For an explanation of the Compact-
SPEECH states see Section 2 3 ) If it is necessary to switch
to power-down mode from any other state the controller
must first issue an S command to switch the Compact-
SPEECH to the IDLE state and then issue the PDM com-
mand Sending any command while in power-down mode
resets the CompactSPEECH detectors and returns the
CompactSPEECH to normal operation mode
1 3 4 Power and Grounding
The CompactSPEECH processor requires a single 5V pow-
er supply applied to the V_CC pins
The grounding connections are made on the GND pins
For optimal noise immunity the power and ground pins
should be connected to V_CC and the ground planes respec-
tively on the printed circuit board If V_CC and the ground
planes are not used single conductors should be run direct-
ly from each V_CC pin to a power point and from each GND
pin to a ground point Avoid daisy-chained connections
Use decoupling capacitors to keep the noise level to a mini-
mum Attach standard 0 1 mF ceramic capacitors to the V_CC
and GND pins as close as possible to the Compact-
SPEECH
When you build a prototype using wire-wrap or other meth-
ods solder the capacitors directly to the power pins of the
CompactSPEECH socket or as close as possible with very
short leads
1 3 5 Memory Interface
Serial Flash Interface
The CompactSPEECH supports up to four NM29A040
4-Mbit or up to two NM29A080 8-Mbit serial flash memory
devices for storing messages
NM29A040
The NM29A040 is organized as 128 blocks of 128 pages
each containing 32 bytes A block is the smallest unit that
can be erased and is 4 kbytes in size
Not all 128 blocks are available for recording Up to 10
blocks may contain bad bits and one block is write-once
and holds the locations of these unusable blocks
For further information about the NM29A040 see the
NM29A040 Datasheet
NM29A080
The NM29A080 is organized as 256 blocks of 128 pages
each containing 32 bytes A block is the smallest unit that
can be erased and is 4 kbytes in size
Not all 256 blocks are available for recording Up to 20
blocks may contain bad bits and two blocks are write-once
and hold the locations of these unusable blocks
For further information about the NM29A080 see the
NM29A080 Datasheet
Message Organization and Recording Time
A CompactSPEECH message uses at least one block The
number of messages that can be stored on one NM29A040
device is 117 – 127 and on one NM29A080 device is 234 to
254 depending on the number of bad blocks The maximum
recording time depends on four factors
The basic compression rate (5 2 kbit s or 7 3 kbit s)
The amount of silence in the recorded speech
The number of unusable blocks
The number of recorded messages (The basic memory
allocation unit for a message is a 4 kbyte block which
means that half a block in average is not used per re-
corded message)
Assuming a single message is recorded in all the available
memory space of a 4 Mbit device with all blocks usable the
maximum recording time using 5 2 kbit s compression is as
follows
TABLE 1-3 Recording Time on 4 Mbit Device
Amount of Silence
Total Record Time
0
13 min 9 sec
10
14 min 25 sec
15
15 min 7 sec
20
15 min 47 sec
25
16 min 25 sec
Serial Flash Endurance
The serial flash may be erased up to 100 000 times To
reduce the effect of this limitation the memory manager
utilizes the serial flash’s blocks evenly i e each block is
erased more or less the same number of times to ensure
that all blocks have the same lifetime
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