APR9600 Aplus Integrated circuits Inc., APR9600 Datasheet - Page 8

• Manufacturer Part Number: APR9600
• Description: Single-chip Voice Recording & Playback Device 60-second Duration
• Manufacturer: Aplus Integrated circuits Inc.

APR9600
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INTEGRATED CIRCUITS INC.
3.2
Microprocessor Controlled Message Management :
The APR9600 device incorporates several features design help simplify microprocessor
Controlled message management When controlling messages the microprocessor
essentially toggles pins as described in the message management sections described
previously. The /BUSY, /STROBE, and /M7_END pins are included to simplify handshaking
between the microprocessor and the APR9600.
The /BUSY pin, when low, indicates to the host processor that the device is busy and that
No commands can be accepted. When this pin is high the device is ready to accept and
execute commands from the host.The /STROBE pin pulses low each time a memory
segment is used. Counting pulses on this pin enables the host processor to accurately
determine how much recording time has been used, and how much recording time
remains. The APR9600 has a total of eighty memory segments.The /M7_END pin is
used as an indicator that the device has stopped its current record or playback operation.
During recording a low going pulse indicates that all memory has been used. During
playback a low pulse indicates that the last message has played.Microprocessor control
can also be used to link several APR9600 devices together in order to increase total
available recording time. In this application both the speaker and microphone signals can
be connected in parallel. The microprocessor will then control which device currently drives
the speaker by enabling or disabling each device using its respective /CE pins.
A continuous message cannot be recorded in multiple devices however because the
transition from one device to the next will incur a delay that is noticeable upon playback.
For this reason it is recommended that message boundaries and device boundaries always
coincide.
3.3 Signal Storage :
The APR9600 samples incoming voice signals and stores the instantaneous voltage
samples in non-volatile FLASH memory cells. Each memory cell can support voltage
ranges from 0 to 256 levels. These 256 discrete voltage levels are the equivalent of 8-bit
(28=256) binary encoded values. During playback the stored signals are retrieved from
memory, smoothed to form a continuous signal, and then amplified before being fed to an
external speaker.
3.4 Sampling Rate & Voice Quality :
According to Shannon's sampling theorem, the highest possible frequency component
introduced to the input of a sampling system must be equal to or less than half the sampling
frequency if aliasing errors are to be eliminated. The APR9600 automatically filters its
input, based on the selected sampling frequency, to meet this requirement.Higher sampling
rates increase the bandwidth and hence the voice quality, but they also use more memory
cells for the same length of recording time.Lower sampling rates use fewer memory cells
and effectively increase the duration capabilities of the device, but they also reduce
incoming signal bandwidth.
The APR9600 accommodates sampling rates as high as 8 kHz and as low a 4 kHz. You
can control the quality/duration trade off by controlling the sampling frequency.
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