J403-6; J403-7; J403-8; J403-11 - Motorola GP68 Service Manual

Theory of Operation
TM
Adaptive Power Control Technology

J403-6

J403-6 is interfaced to pin 4 of voltage regulator U456. This
is the microprocessors 5 V source from the main board to the
option board. Maximum current sourcing is 100 mA. Regu-
lation is ± 0.2 Vdc.

J403-7

J403-7 interfaces with pin 52 of U401. Pin 52 of the micro-
controller is bi-directional port D bit 3. In the GP60 Series
Radio, this connection is for serial data out of the microcon-
troller. This controls loading of the various electrical sub-
systems internal to the radio in addition to data required by
option boards installed into the radio. For option connector
purposes this pin is used to shift multi-byte messages from
the radio to an option board. When used for this purpose, pin
J403-2 option board enable, is driven low by the radio micro-
controller to enable a serial byte transfer to an option board.

J403-8

J403-8 interfaces with pin 51 of U401, the radio microcon-
troller. Pin 51 of the microcontroller is bi-directional port D
bit 2. In the GP60 Series Radio, this is decoder data into the
radio. On a DTMF decoder board this would be the serial
input for the 4-bits of tone data. On other option boards this
input is used as the serial input for a multiple byte message.
J403-9
This option interface pin is connected to the Rx Out signal,
pin 23 of the Audio Filter IC, U451 through coupling capac-
itor C450. In the GP60 Series Radio, this signal de-empha-
sizes Rx audio and output is always unmuted audio in the
radio. This pin may be used as the receive audio to a decoder
option board such as DTMF, Two Tone Sequential, or MSK
signalling decode. An audio scrambler option board may
also use this input for receive audio in. Any option board
requiring pre-emphasized audio would have to include the
necessary filtering. The level of this de-emphasized audio is
450 mV rms at 15 ohm impedance.
J403-10
This is the Rx audio output of the option board. This connec-
tion may be used for option boards that need to enable Rx
audio on signaling decodes or to descramble audio as
required by the option board descrambling technique. Option
board Rx audio input is available at J403-10 with a sensitiv-
ity of 100 mV rms at less than 200 ohm output impedance
from an option board. R480, a 30k ohm resistor between
option board pins J403-9 and J403-10 requires design con-
sideration on the part of any option board using Rx audio
output. The Rx audio output level is controlled by the GP60
Series Radio volume control before the audio amp.

J403-11

J403-11 interfaces with pin 53 of U401. Pin 53 of the micro-
controller is bi-directional port PD5. In the GP60 Series
2-4
Radio, this is the CLOCK output from the microcontroller
for loading all internal subsystems as well as option boards
that require synchronous serial transfers. Option boards
requiring a multi-byte transfer may use this output as the
CLOCK source for uploading internal option board registers
on power-up, channel change, or for reading serial control
requests.
J403-12 interfaces with pin 63 of U401. Pin 63 of the micro-
controller is an input on port A bit 2 of the radio microcon-
troller. In the GP60 Series Radio, this connection is used for
a variety of input signals from an option board. In a simple
option board configuration, a falling edge on this pin connec-
tion signals that a selective call has been decoded by the
option board. For DTMF decoder boards or other simple
BCD decoder boards, a falling edge on this pin indicates that
a digit decode has been completed and is ready to be shifted
into the microcomputer for concatenation and comparison to
an ID string. In more complex option boards, a falling edge
on this pin indicates that an option board requests a serial
transfer on J403-8 and J403-1 or an acknowledgment of data
received on J403-7 in a multiple byte transfer.
Adaptive Power Control
Technology
The GP60 Series Radio power control is specially designed
to handle alkaline battery voltage and current characteristics,
without compromising output power variation when used
with NiCd batteries.
Basically there are three sections of the power control cir-
cuitry. Digital to analog converter, voltage to current con-
verter and the cut back circuitry that react on alkaline
batteries.
Digital to analog converter consists of shift register U152,
R166, R167, R168, R169 and R170. These are the discrete
components that make the resistor ladder digital to analog
converter. The output of the DAC is in a form of a voltage.
Since the power levelling on the rf board requires current as
a reference, this voltage has to be converted into current.
Voltage to current converter consists of U150-2, and Q101.
This is a standard voltage to current converter.Since the oper-
ational amplifier cannot work at zero volt input, reference
zero level has been shifted to around 1.5 volt on operational
amplifier input by R173 and R174. The DAC voltage also is
shifted accordingly by R172. The output of this section will
go to the power levelling circuit on the rf board. A delay
capacitor is added (C169) to ensure that DAC voltage will
appear only after TXB+. A fast discharge transistor (Q404)
is needed to ensure that the capacitor is fully discharged
before transmitting.
The cut back circuitry (U150-1 circuitry) is used to protect
the radio from operating beyond the capability of the supply
voltage especially when radio is powered by alkaline batter-
ies. Alkaline batteries have higher internal resistance and
6881086C09-O
GP68 Portable Radios Service Manual

J403-12

TM
March, 1997