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NSAM266SVLJ Datasheet(PDF) 8 Page - National Semiconductor (TI) |
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NSAM266SVLJ Datasheet(HTML) 8 Page - National Semiconductor (TI) |
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8 / 52 page  10 Hardware (Continued) 133 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 15 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 210 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 VCC b 05V or below VSS a 05V 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 214) It may only be issued when the CompactSPEECH is in the IDLE state (For an explanation of the Compact- SPEECH states see Section 23) 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 134 Power and Grounding The CompactSPEECH processor requires a single 5V pow- er supply applied to the VCC pins The grounding connections are made on the GND pins For optimal noise immunity the power and ground pins should be connected to VCC and the ground planes respec- tively on the printed circuit board If VCC and the ground planes are not used single conductors should be run direct- ly from each VCC 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 01 mF ceramic capacitors to the VCC 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 135 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 (52 kbits or 73 kbits) 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 52 kbits 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 100000 times To reduce the effect of this limitation the memory manager utilizes the serial flash’s blocks evenly ie each block is erased more or less the same number of times to ensure that all blocks have the same lifetime http www nationalcom 8 |
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