Product Data Sheets

ISD1000A Series

1–4

Chip Enable Input (CE)

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.

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).

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

the event of a message overflow (device full).

In addition, the ISD1000A Series has an internal

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.

Microphone Input (MIC)

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.

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-

DISCONNECTED

.

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 K

Ω internal

resistance and an external capacitor (C2) con-

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

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.

06.DataBook_1000A Dsht Page 4 Friday, September 27, 1996 10:44 AM