Rainbow Electronics ISD4004 - Manual (Page 8)

ISD4004 Series
4 Voice Solutions in Silicon ™
ROW ADDRESS CLOCK (RAC)
This is an open drain output pin that provides a sig-
nal with a 200 ms period at the 8 KHz sampling fre-
quency. (This represents a single row of memory
and there are 2400 rows of memory in the ISD4004
series devices.) This signal stays HIGH for 175 ms
and stays LOW for 25 ms when it reaches the end
of a row.
The RAC pin stays HIGH for 109.38
msec and stays
LOW for 15.63
msec in Message Cueing mode
(see page 5 for a more detailed description of
Message Cueing). Refer to the AC Parameters ta-
ble for RAC timing information on other sample
rate products.
When a record command is first initiated, the RAC
pin remains HIGH for an extra T
RACLO
period. This is
due to the need to load sample and hold circuits
internal to the device. This pin can be used for
message management techniques.
EXTERNAL CLOCK INPUT (XCLK)
The external clock input for the ISD4004 products
has an internal pull-down device. These products
are configured at the factory with an internal sam-
pling clock frequency centered to ±1 percent of
specification. The frequency is then maintained to
a variation over the entire commercial tempera-
ture and operating voltage ranges as defined by
the minimum/maximum limits in the applicable
AC Parameters table. The internal clock has a tol-
erance, over the extended temperature, industrial
temperature and voltage ranges as defined by the
minimum/maximum limits in the applicable AC
Parameters table. A regulated power supply is
recommended for industrial temperature range
parts. If greater precision is required, the device
can be clocked through the XCLK pin in Table 1.
These recommended clock rates should not be
varied because the antialiasing and smoothing filters
are fixed. Thus, aliasing problems can occur if the
sample rate differs from the one recommended.
The duty cycle on the input clock is not critical, as
the clock is immediately divided by two internally.
If the XCLK is not used, this input should be
connected to ground.
AUTOMUTE™ FEATURE (AM CAP)
This pin is used in controlling the AutoMute feature.
The AutoMute feature attenuates the signal when
it drops below an internally set threshold. This helps
to eliminate noise (with 6 dB of attenuation) when
there is no signal (i.e., during periods of silence). A
1
mF capacitor to ground should be connected to
the AM CAP pin. This capacitor becomes a part of
an internal peak detector which senses the signal
amplitude (peak). This peak level is compared to
an internally set threshold to determine the Auto-
Mute trip point. For large signals the AutoMute at-
tenuation is set to 0 dB while 6 dB of attenuation
occurs for silence. The 1
mF capacitor also affects
the rate at which the AutoMute feature changes
with the signal amplitude (or the attack time). The
Automute feature can be disabled by connecting
the AM CAP pin to V
CCA
.
Table 1: External Clock Input Clocking
Table
Part Number Sample Rate Required Clock
ISD4004-08M 8.0 KHz 1024 KHz
ISD4004-10M 6.4 KHz 819.2 KHz
ISD4004-12M 5.3 KHz 682.7 KHz
ISD4004-16M 4.0 KHz 512 KHz