User guide

Voice Recording & Playback Device Page 13
Revision 2.1
Playing Back Audio Data
When a
SET_PLAY
or
PLAY
command is issued the device
will be
gin sampling the data in the specified sector and pro-
duce a resultant output on the AUDOUT, ANAOUT-, and
ANAOUT+ pins. After half the sector is used the SAC pin will
drop low to indicate that a new command can be accepted.
The device will accept commands as lon
g as the SAC pin
remains low. An
y command received after the SAC returns
hi
gh will be queued up and executed during the next SAC
c
ycle.
Fi
gure 14 shows a typical timing diagram and OpCode
se
quence for a playback operation. The
SET_PLAY
com-
mand be
gins playback at the specified memory location after
T
aplay
time has passed. Some time later the low going edge
on the SAC pin alerts the host processor that half of the first
sector has been pla
yed back. The host processor responds
b
y issuing a
PLAY
command during the SAC low time. The
PLAY
command instructs the APR6008 to continue playback
of the sector immediatel
y following the current sector. When
the first sector has been pla
yed back the device jumps to the
next sector and returns the SAC si
gnal to a high state to indi-
cate that the second sector is now bein
g played. At this point
the host processor decides to issue a
STOP
command during
the next available SAC low time. The device follows the
STOP
command and terminates playback after TS
aplay
. The /
BUSY pin indicates when actual pla
yback is taking place.
Figure 14 Typical Playback Sequence
Handshaking signals
Several signals are included in the device that allow for hand-
shakin
g. These signals can simplify message management
si
gnificantly depending on the message management
scheme used.
The /INT si
gnal can be used to generate interrupts to the pro-
cessor when attention is re
quired by the APR6008 This pin is
normall
y high and goes low when an interrupt is requested.
An interrupt is
generated whenever a EOD or Overflow
occurs. An interrupt is also
generated after a PWRUP com-
mand if a low batter
y VCC is sensed.
The SAC si
gnal is used to determine when the device is
nearin
g the end of the current memory segment during either
a record, pla
y or forward operation. The SAC signal is in a
normall
y high state. The signal goes low after half the cur-
rentl
y active segment has been played or recorded. The sig-
nal returns to a hi
gh state after the entire segment has been
pla
yed or recorded. The microprocessor should sense the
/CS
SCLK
DI
T
aplay
TS
aplay
SET_PLAY
STOP
SAC
ANAOUT+
ANAOUT-
ANAOUT
/BUSY
Note: Command timing is not scale
PLAY
APR6008