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NSAM265SR Datasheet(PDF) 8 Page - National Semiconductor (TI) |
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NSAM265SR Datasheet(HTML) 8 Page - National Semiconductor (TI) |
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8 / 58 page  10 Theory of Operation (Continued) 173 Memory Operating Modes in NSAM265SF The NSAM265SF supports two operating modes of the FLASH memory manager (selected by the CFG command) Normal Mode In this mode the NSAM265SF always keeps one free block for memory management The EV MEMFULL event is set when all but one good AFLASH blocks are full and record- ing on the last available free block is not allowed Maximum recording time in this mode On one 8-Mbit FLASH (no bad blocks) device 28 minutes and 8 seconds On one 4-Mbit FLASH (no bad blocks) device 13 minutes and 8 seconds Memory Intensive Mode All good blocks are available for message recording As long as there is one free block available for memory man- agement this mode is the same as normal mode The Com- pactSPEECH sets the EV MEMLOW event when approxi- mately 20 seconds recording time remain on the one-be- fore-last FLASH block The EV MEMFULL event is set only when all the blocks are full However if the last good block is used for recording the NSAM265SF no longer has a free block for memory man- agement and therefore may fail to free memory space ie execute the FR command The microcontroller must delete all messages with the MESSAGE SAFE bit cleared to guarantee that at least one block is erased and can be used for memory management When there is no block available for memory management and you attempt to record a message with the MESSAGE SAFE bit set the CompactSPEECH sets the EV MEMFULL event and does not allow you to record Thus it is possible to avoid a situation where a safe message must be deleted to free a FLASH block Maximum recording time in this mode On one 8 Mbits FLASH (no bad blocks) device 30 minutes On one 4 Mbits FLASH (no bad blocks) device 15 minutes 18 TONE AND NO-ENERGY DETECTION The CompactSPEECH detects DTMF busy and dial tones and no energy (VOX) This enables remote control opera- tions and call progress Detection is active throughout the operation of the CompactSPEECH Detection can be con- figured using the SDET (Set Detectors Mask) command which controls the reporting of occurrence of tones and the RDET (Reset Detectors) command which resets the detec- tors DTMF DTMF detection may be reported at starting point ending point or both The report is made through the status word (for further details see GSW command in Section 32) The DTMF detector specifications as measured on the line input using the NSV-AM265-DAA board are summarized be- low (see Table 1-2) Echo Cancellation Echo cancellation is a technique used to improve the per- formance of DTMF tone detection during speech synthesis tone generation and OGM playback For echo cancellation to work properly AGC must not be active in parallel Thus to take advantage of echo cancellation the microcontroller must control the AGC ie disable the AGC during PLAY SYNTHESIS and TONE GENERATE states and enable it again afterwards If AGC can not be disabled do not use echo cancellation The microcontroller should use the CFG command to activatedeactivate echo cancellation (For fur- ther details see Section 32) Echo cancellation applies only to DTMF tones Busy and dial tones detection is not affected by this technique TABLE 1-2 DTMF Detector Specifications Play Record Idle Detection Sensitivity b 33 with Echo Canceller b 40 dBm (Note A) b 23 wo Echo Canceller Accepted l 50 ms l 40 ms DTMF Length Frequency Tolerance g 15% g 15% SN Ratio 12 dB 12 dB Minimum Spacing l 45 ms l 45 ms (Note B) Normal Twist 8 dB 8 dB Reverse Twist 4 dB or 8 dB 4 dB or 8 dB (Note C) Note A Performance depends on DAA design Note B If the interval between two consecutive DTMF tones is less than or equal to 20 ms the two are detected as one long DTMF tone If the interval between two consecutive DTMF tones is between 20 ms and 45 ms sepa- rate detection is unpredictable Note C Determined according to the DTMF REV TWIST tunable param- eter value 8 |
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