2-8
Theory
of
Operation
U0101-69 is the high reference voltage for the AID ports on the
IJP.
Capacitor C0101 filters the +5
volt reference. If this voltage
is
lower than +5 volt,
theA/Dreading
is
incorrect. Likewise
U01
01, pin
68
is
the low reference for the A/D ports. This line is normally tied to ground. If this line
is
not
connected to ground, the AID readings could be incorrect.
2.2.11 Static Random Access Memory (SRAM)
The SRAM (U0121) contains temporary radio calculations or parameters that can change very
frequently, and which are generated and stored by the software during its normal operation. The
information is lost when the radio is turned off.
The device allows
an
unlimited number
of
write cycles. SRAM accesses are indicated by the CS
signal U0122, pin 20 which is the result
of
U01
01-CSGP2 going
low.
U0122 is commonly referred to
as the external RAM as opposed to the internal RAM which is the 3 KBs
of
RAM (part
of
the
68HC11FLO). Both RAM spaces serve the purpose. However, the internal RAM is used for the
calculated values which are accessed most often.
Capacitor
C0122 filters out any ac noise which may ride on +5V at U0122.
2.3 Controller Board Audio and Signalling Circuits
2.3.1
Audio Signalling Filter
IC
with Compander (ASFIC CMP)
The ASFIC CMP (U0221) used
in
the controller has the four following functions:
RX/TX audio shaping, i.e. filtering, amplification, attenuation
RX/TX signalling, PL/DPL/HST/MDC
Squelch detection
11P
clock signal generation
The ASFIC CMP is programmable through the SPI BUS (U0221-20/21/22), normally receiving 19
bytes. This programming sets up various paths within the ASFIC CMP to route audio and/or
signalling signals through the appropriate filtering, gain, and attenuator blocks. The ASFIC CMP
also has six general control bits (GCB0-5) which are CMOS level outputs and used for NOISE
BLANKER (GCBO)
in
low band radios, EXTERNAL ALARM (GCB1), and DC POWER ON (GCB2)
to switch the voltage regulators (and the radio) on and off. GCB3 controls U0251, pin
11
to output
either RX FLAT AUDIO or RX FILTERED AUDIO on the accessory connector, pin 11. GCB4 controls
U0251,
pin 10 to use either the external microphone input or the voice storage playback signal.
GCB5 switches the audio
PA
on and off.
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