Kenwood TM-731A Service Manual page 16

TM-731A/E
16
CIRCUIT DESCRIPTION
® Tone Output
Signals from pins P40 to P43 and P50 to P53 of the
microprocessor are fed to a ladder resistor network (IC104)
which performs D-A conversion and provides 38 signals rang-
ing from 67.0 to 250.3. ;
Fig. 24 shows the internal structure of 1C104.
x2
o>
10 =J 20K fr
pF —t— P42
xo
os
7 20K j 20K Ig
—wg—— PS!
x
so]
12 20K 20K Is
at P40
een
Tone output g—
Fig. 24 Ladder Network: Internal Structure of KRR-CO0O1
(Control Unit IC 104)
¢ S meter and RF meter input
The S meter and RF meter voltages are coupled separately for
the main band and subband and are provided as the M1 and
M2 inputs to the PTHOO and PTHO1 pins of the microprocessor.
The input voltage is converted internally to a 4-bit digital value
(16 levels) and sent to the display.
© Busy. Inputerr. eeecceure
BUSY signals are supplied separately to the microprocessor
for the main band and subband. if squelch is on, the
microprocessor receives a Low input when the received sig-
nal is present, and lights the BUSY indicator.
¢ Input and Output for CTCSS Unit (Option)
The microprocessor provides data for the CTCSS unit from pins
P70, P71, and P73. This data specifies the CTCSS tone fre-
quency and CTCSS unit on/off information.
When a tone is detected from the CTCSS unit, the microproces-
sor receives a High input at P121.and opens the squelch gate.
from IC3 6 pin
CTCSS MAIN/SUB select
when "L"' level: MAIN
from SUB RD
(RDS)
to AIM r
15
ee
(o)
4& from MAIN RD
(RDM)
* Input and Output for Remote Control Unit (RC-10, Option)
When the remote control unit is connected, the microproces-
sor receives a High input at P123 and switches the following
pin functions:
PO3 -SI___: Serial data input pin
PO2 +~SO_ : Serial data output pin
PO1 >SCK : Serial clock input/output pin
Data transfer between the microprocessor in the set and the
microprocessor in the remote control unit takes place over these
lines.