ISD1000A Series
Product Data Sheets
Chip Enable Input (CE)
Microphone Input (MIC)
The CE pin is taken LOW to enable all Playback
and Record operations. The address inputs and
Playback/Record input (P/R) are latched by the
falling edge of CE. When CE is taken HIGH, the
ISD1000A is unselected, the P/R is HIGH, and the
auxiliary input is directed into the speaker ampli-
fier.
The microphone input transfers its signal to the
on-chip preamplifier. An on-chip Automatic Gain
Control (AGC) circuit controls the gain of this
preamplifier from -15 to 24 dB. An external micro-
phone should be AC coupled to this pin via a
series capacitor. The capacitor value, together
with the internal 10 Kohm resistance on this pin,
determines the low-frequency cutoff for the
ISD1000A Series passband. See ISD’s Applica-
tion Notes and Design Manual in this book for
additional information on low-frequency cutoff cal-
culation.
Playback/Record Input (P/R)
The P/R input is latched by the falling edge of the
CE pin. A HIGH level selects a Playback cycle
while a LOW level selects a Record cycle. For a
Record cycle, the address inputs provide the
starting address and recording continues until PD
or CE is pulled HIGH or an overflow is detected
(i.e. the chip is full). When a Record cycle is termi-
nated by pulling PD or CE HIGH, an End-Of-Mes-
sage (EOM) marker is stored at the current
address in memory. For a Playback cycle, the
address inputs provide the starting address and
the device will play until an EOM marker is
encountered. The device can continue past an
EOM marker in an operational mode, or if CE is
held LOW in address mode. (See page 1-6 for
more Operational Modes).
Microphone Reference Input (MIC REF)
The MIC REF input is the inverting input to the
microphone preamplifier. This provides a noise-
canceling or common-mode rejection input to the
device when connected to a differential micro-
phone. IF THIS INPUT IS UNUSED, IT MUST BE LEFT
DISCONNECTED.
-1
Automatic Gain Control Input (AGC)
The AGC dynamically adjusts the gain of the
preamplifier to compensate for the wide range of
microphone input levels. The AGC allows the full
range of whispers to loud sounds to be recorded
with minimal distortion. The “attack” time is deter-
mined by the time constant of a 5 KΩ internal
resistance and an external capacitor (C2) con-
End-Of-Message Output (EOM)
A non-volatile marker is automatically inserted at
the end of each recorded message. It remains
there until the message is recorded over. During
Playback, the EOM output pulses LOW for a
nected from the AGC pin to V
analog ground.
SSA
The “release” time is determined by the time con-
stant of an external resistor (R2) and an external
capacitor (C2 on the schematic on page 1-17)
connected in parallel between the AGC Pin and
period of T
at the end of each message, or in
EOM
the event of a message overflow (device full).
In addition, the ISD1000A Series has an internal
V
analog ground. Nominal values of 470 KΩ
SSA
V
detect circuit to maintain message integrity
CC
and 4.7 µF give satisfactory results, in most cases.
For AGC voltages of 1.5V and below, the pream-
plifier is at its maximum gain of 24 dB. Reduction
in preamplifier gain occurs for voltages of approx-
imately 1.8V.
should V
fall below 3.5V. In this case, EOM
CC
goes LOW and the device is fixed in Playback-
only mode. The EOM marker provides a conve-
nient handshake signal for a processor, and also
facilitates the cascading of devices.
1 –4
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