Motorola HT 1000 series Theory/Troubleshooting Manual page 26

2. Microcomputer Clock Synthesizer
Upon power-up, and assuming that the ASF IC
receives a proper 2.1MHz input at U701 pin 33
(which comes from the transceiver board), the ASF
IC outputs a 3.6864MHz CMOS square wave on
U701 pin 35. This UP CLK signal connects to the
input of the microcomputer (U705 pin 77) as
EXTAL. The microcomputer operates at 1/4 of this
frequency, which in this case computes to
921.6KHz.
After initialization, upon power-up, the microcomput-
er programs the ASF IC to change the E-clock to
1.9872 MHz. Therefore, soon after the controller is
powered up, serial data is sent to the ASF IC on sig-
nal line U701 pin 32, while select line U701 pin 30 is
held low. The result is a 7.9488MHz clock signal (4x
1.9872MHz) on U701 pin 35.
3. SB9600 Serial Interface
The radio uses a proprietary multiprocessor serial
protocol known as SB9600. This protocol allows the
microcomputer in the system to interface with an
external personal computer (PC) for RSS program-
ming, a remote hand-held mic, or a vehicular
adapter.
From a hardware standpoint, the external interface
is the universal side connector, BUSY and DATA
lines (P403 pins 9 and 13 respectively). The DATA
signal is a bidirectional 0-5V RS-232 line that uses
U705's integrated RS-232 asynchronous serial
communication interface (SCI) peripheral. The SCI
TX line is U705-PD1 and the SCI RX line is U705-
PD0. The SCI TX line and the SCI RX line are
connected together, thus providing the DATA signal,
which is routed to the controller connector jack,
J701 pin 26. The BUSY signal (at U705 pin 8, PA3)
is an active-high bidirectional signal that is normally
pulled down by 10K resistor R737. The BUSY signal
is routed to the controller connector jack, J701
pin 22.
A typical usage of the SB9600 interface occurs
when using a PC to run the RSS software package
and the radio interface box (RIB) to program the
radio's codeplug. When the PC sends a command
or data to the radio, observe the SCI RX line (U705
pin 82, PD0) toggling at a 9600 baud rate and the
BUSY line going high when data is actually being
sent. After the data transfer is complete, the busy
line should idle low and the LH DATA line should
idle high. The controller board also sends a power-
up status message when it is first turned on. The
SB9600 data being sent from the radio can be
observed within a few msec. after power-up.
4. SPI Interface
The microcomputer communicates to several ICs
and modules through a dedicated on-chip SPI port,
18
which consists of a transmit data line (U705 pin 1,
PD3), a receive data line (U705 pin 84, PD2), and a
clock line (U705 pin 2, PD4). In addition, each IC
that can be accessed by the microcomputer, using
the SPI, has a select line associated with it. The
programmable ICs or circuits and their associated
select lines are:
• ASF IC (U701) - select line at U701 pin 30
• transceiver board reference oscillator (U203) -
select line at U203 pin 24
• transceiver board synthesizer (U204) - select
line at U204 pin 4
• transceiver board I-F (U3) - select line at U3
pin 21
• transceiver board D/A IC (U102) - select line at
U102 pin 16
The select lines for all of the SPI devices listed are
active low; i.e., the select line goes low when the
associated device is being programmed.
5. Option Select Lines
The two option select lines, OPT SEL 1 and OPT
SEL 2 (P403 pins 1 and 5, respectively), are used to
identify the presence of external accessories and
also to key up the radio with an external micro-
phone. Table 1 shows the function and the two
associated signal states sensed by the microcom-
puter at U705 pins 38 and 37. Both signals have
pull-up resistors inside the microcomputer, so that if
no external device is connected to these pins, they
will be at a logic high level and the radio will be in
the normal mode; i.e., internal speaker and micro-
phone will be used.
Radio frequency power will always be routed to the
internal antenna port, unless a side connector is
installed that mechanically activates RF switch
S101, which redirects power to the external antenna
port. The microcomputer has no knowledge or con-
trol of which port RF energy is being directed. An
external PTT [OPT SEL 1 = 0 (low), OPT SEL 2 = 0
(low)], will cause the external mic audio port to be
activated, but the RF could be routed through either
RF port.
Table 1. Option Select Definition
OPT SEL 1 OPT SEL 2
High High
Low High
Low Low
High Low
6. LED Control
The bicolor LED (CR702A and CR702B) is activat-
ed by microcomputer U705 in conjunction with the
FUNCTION
Normal
External Speaker
External PTT
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