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secure board it is decrypted and converted
back to analog format, and then fed back to the
ASF IC from the AUX RX line (J702 pin 9). It is
then routed to the ASF IC pin U701-J6; from
then on it traverses a path identical to conven-
tional receive audio
4. Receive Data Circuits
The ASF IC (U701) decodes all receive data, which
includes PL, DPL, low-speed trunking, MDC, and
high-speed trunking data. The "decode" process for
each data type typically involves low-pass or band-
pass filtering, signal amplification, and then routing
the signal to a comparator, which outputs a logic
zero or one signal. The discriminator output from
the transceiver board is routed to U701-J7 through
coupling capacitor C709. Inside U701, the data is fil-
tered according to the data type (HS data or LS
data), then hard-limited to a 0–5V digital level. The
high-speed limited data output (MDC and trunking
high-speed) appears at U701-G4, where it connects
to U705-PA0. The low-speed limited data output
(PL, DPL and trunking low-speed) appears at U701-
A4, where it connects to U710-PK7. If, for example,
the radio is receiving 192.8Hz PL, the discriminator
should contain a 192.8Hz sine wave at about
53mVrms, and the limited PL output should be a
192.8 Hz square wave. While the radio is decoding
PL, DPL, or low-speed trunking data, the micropro-
cessor also outputs a sampling waveform on
U705-PA6, which is routed to U701-C3. (This is the
same line used to generate TX PL or DPL data.)
This sampling waveform is a square wave between
1000 and 2000Hz.
5. Alert Tone Circuits
When the microprocessor needs to give the opera-
tor feedback (for a good key press or for a bad key
press) or radio status (trunked system busy, low
battery condition, phone call, circuit failures), it
sends an alert tone to the speaker. It does so by
sending data to U701, which sets up the audio path
to the speaker for alert tones. The alert tone itself
can be generated in one of two ways: internally by
the ASF IC, or externally using the microcontroller
and the ASF IC. The allowable internal alert tones
are 300, 900, and 1800Hz. For external alert tones,
the microcontroller can generate any tone within the
100-3000Hz audio band. This is accomplished by
the microprocessor toggling the output line U705-
PA4, which is also the same line used to generate
low-group DTMF data. Inside the ASF IC, this signal
is routed to the external input of the alert tone gen-
erator. The output of the generator is summed into
the audio chain just after the RX audio de-emphasis
block. Inside U701, the tone is amplified and fil-
tered, then passed through the 8-bit digital volume
28
attenuator. (Note that the expander is bypassed
even if U601 is present.) The tone exits at U701-J4,
then is routed to the audio PA the same as receive
audio.
VII. UNIVERSAL CONNECTOR (See Tables 2 and 3)
The universal connector (radio side connector) con-
sists of 13 pins, many of which serve multiple functions.
The various pins will be discussed by function.
Pins 1 and 5 are the option selection lines, OPT
SEL 1 and OPT SEL 2, respectively. The state of these
pins informs the radio microcontroller of the type of
accessory attached, and the operating mode of the
accessory. For example, an external speaker micro-
phone will select external speaker by pulling OPT SEL 1
low, and will indicate PTT by pulling both OPT SEL 1
and OPT SEL 2 low. Refer to Table 2 for details.
Pin 2, the EXT SPKR line, and pin 6, the SPKR
COMM line, provide the two signals required for the dif-
ferentially driven external speaker.
Pin 3, the EXT MIC line, is used for external micro-
phone audio.
Pin 4, the OPT B+/BOOT PGM SEL pin, serves two
functions. This pin is normally used to provide current
limited SW B+ to an external accessory. For special pur-
poses, most commonly reprogramming the Flash
memory in the radio, this pin serves another function.
This pin is also able to put the microprocessor in a spe-
cial "bootstrap" mode. This allows software to be loaded
into the processor to reprogram the Flash memory
device.
Pin 7, the AUX TX/RSSI/RX OUT/DVP WE/RTS
pin, serves many functions depending on the radio
mode of operation. This pin is multiplexed by the MUX
(U711), the ASF IC (U702), and the SLIC, U710. This
pin serves as an analog input for AUX TX when used for
modulation balance adjustments when programmed by
the RSS. It serves as an analog output of RSSI informa-
tion when tuning front-end filters in UHF and VHF radios
when programmed by the RSS. It serves as an analog
output of buffered discriminator signal when tuning dis-
criminator level with the RSS (secure equipped radios).
It serves as a digital input for the key-variable loader
(KVL) WE signal when the key-variable loader is
attached.
Pin 8 is controller board ground. This is an indepen-
dent ground path from the RF ground, which is also on
the universal connector.
Pin 9, the LH BUSY/KID/DATA IN line, serves sev-
eral functions. During normal radio operation, this pin is
used for the BUSY signal for SB9600 communications.
When a key-variable loader is attached, this pin carries
the key insert data (KID) signal.
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Troubleshooting
