3.2.4.5
RADIO INTERFACE TO MICROPROCESSOR
The interface between the radio system and the microprocessor occurs in three ways, by the
microprocessor directly, by the microprocessor serial control bus, or by the serial latch IC207.
The microprocessor port connections are configured as either; inputs only, outputs only, or, in
the case of the serial bus, as a bi-directional port.
The following is a description of the ports and their allocated function:
P0.0
Keyboard row 1
P0. 1
Keyboard row 2
P0.2
Keyboard row 3
P0.3
Microphone cradle input
P0.4
Microphone PTT input
P0.5
Hardware mute input
P0.6
Synthesizer out-of-lock input
P0.7
CTCSS detect input
All the above port lines are configured as inputs.
Lines P0.0, P0. 1 and P0.2 are used to read to which row the pressed key belongs. This is
used in conjunction with ports P3.5, P3.6 and P3.7.
Line P0.3 comes from the microphone socket pin 3 via a suppression network consisting of
C269, R281 and R277. This input is active low ie: a 0V level indicates microphone-in-cradle.
Line P0.4 comes from the microphone socket pin 4 via a suppression network consisting of
C270, R282 and R278. This input is active low, ie: a 0V level indicates transmit, and a high
level 5V indicates receive.
Line P0.5 comes from the hardware mute detector circuit. It is used to indicate to the control
program the presence or not of an RF carrier on the channel, ie: a 0V level indicates no RF
carrier.
Line P0.6 is the phase locked loop synthesizer out-of-lock indicator line. This signal comes
from IC403 on the radio PCB and indicates to the control program whether or not the
synthesizer is in-lock, ie: a 0V level indicates in-lock.
Line P0.7 is derived from the CTCSS encoder/ decoder IC204. This signal indicates that the
CTCSS decoder is decoding the correct sub-audible tone, ie: a 0V level indicates CTCSS
decode.
P1.0
Serial control bus data line
P1.1
Serial control bus clock line
P 1.2
LCD display driver enable
P1.3
PLL synthesizer program enable
P 1.4
EEPROM enable
P 1.5
CTCSS encoder/decoder enable
P1.6
Radio latch enable
P1.7
Radio latch output enable
Section 3 Page 21
