CIRCUIT DESCRIPTION
6-11
August 1993
Part No. 001-9750-001
amplifier U504D. The base voltage of Q502 is
controlled by current sense amplifier Q506 and a D-A
converter formed by shift register U503 and a resistor
network.
As the voltage from the D-A converter increases,
Q502 and Q511 turn on more which causes power
output to increase. If current becomes excessive, Q506
turns on more which lowers the base voltage of Q502
and lowers power output. If forward or reverse power
increase, the output of summing amplifier U504D
increases. This increases the emitter voltage of Q502
which then turns off more and lowers power output.
C584 delays power output for a few milliseconds to
stabilize the power control loop. C540 provides nega-
tive feedback to stabilize the circuit.
Shift register U503 controls the output voltage to
the power control circuit by changing the logic levels
applied to the resistor network connected to the O0-O6
pins. It also controls transmit switch Q507/Q514
which is connected to the Q7 pin. R558 and C565
form an RC network which prevents momentary
power output when transceiver power is turned on.
These components hold the OE (output enable) input
low for a short time which disables the O0-O7 outputs.
6.5 AUDIO/LOGIC BOARD DIGITAL CIRCUIT
DESCRIPTION
6.5.1 MICROPROCESSOR (U401)
General
The control logic for this transceiver is based on
an MC68HCP11A0 eight-bit microprocessor. This
particular device has an internal 256-byte static RAM
but no internal ROM or EEPROM. Therefore, all
program memory is stored in external memory
devices. Besides several general purpose inputs and
outputs, this device has an eight-channel A/D (analog-
to-digital) converter and synchronous and asynchro-
nous serial ports. The A/D converter allows it to
monitor analog voltages such as the 13.8-volt supply
and the transmitter temperature.
The microprocessor operates in the expanded
mode which is selected by a high level on the MODA
and MODB pins. This mode allows external memory
and peripheral devices to be accessed by a multiplexed
address/data bus. Multiplexing allows the eight pins of
the data bus (AD0-AD7) to be used for memory
addressing as well as data input and output. For more
information, see “Address/Data Bus” description
which follows.
The operating speed of the microprocessor is set
by crystal Y300. The 8 MHz frequency of this crystal
is divided by four by an internal divider to produce as
internal operating frequency of 2 MHz.
Memory
The operating program is stored in external flash
EPROM U404. This is a 128K x 8 memory device
which contains the instructions used by the micropro-
cessor to provide transceiver control. The use of a
flash EPROM allows the operating program to be
updated using the standard programming setup and
special software. This eliminates the need to remove
the transceiver and change a ROM or the micropro-
cessor to update software. When reprogramming of
this EPROM occurs, the MODA/ MODB inputs of the
microprocessor are pulled low to put it in a special
bootstrap mode. In addition, a 12 VDC Vpp voltage
generated by the RPI is applied to U404.
Information which changes from transceiver to
transceiver is stored in EEPROM (electrical erasable
memory) U406. This device contains the information
loaded into the transceiver by the personal computer
programming described in Section 4. An EEPROM
can be reprogrammed by the microprocessor many
times, and it maintains stored data without the need for
a continuous power supply.
CAUTION:
EEPROM U406 is not replaceable
because it is cemented to the PC board. Attempting to
remove this part may seriously damage the board.
Temporary data storage is provided by RAM
U405. This device is used as a “scratchpad” by the
microprocessor while it is controlling the transceiver.
This is a static-type RAM which means that it does not
require periodic refreshing to maintain its contents.
However, the data is lost when transceiver power is
turned off.
Reset
The microprocessor is reset when transceiver
power is turned on and also when the 5-volt supply
Summary of Contents for Summit DM 975x
Page 105: ...MULTI NET SYSTEM OVERVIEW 5 10 Revised February 1997 Part No 001 9750 005 ...
Page 108: ...CIRCUIT DESCRIPTION 6 3 August 1993 Part No 001 9750 001 Figure 6 1 Transceiver Block Diagram ...
Page 123: ...CIRCUIT DESCRIPTION 6 18 August 1993 Part No 001 9750 001 ...
Page 131: ...SERVICING 7 8 Revised January 1995 Part No 001 9750 003 ...
Page 156: ...9 19 Revised December 2000 Part No 001 9750 007 TRANSCEIVER EXPLODED VIEW PART 1 ...
Page 168: ...Revised January 1995 Part No 001 9750 003 10 11 INTERCONNECT SCHEMATIC ...
Page 169: ...Revised January 1995 Part No 001 9750 003 10 12 DISPLAY BOARD SCHEMATIC ...
Page 171: ...Revised January 1995 Part No 001 9750 003 10 14 RF BOARD SCHEMATIC REVISED 800 MHZ ...
Page 172: ...Revised January 1995 Part No 001 9750 003 10 15 RF BOARD BOARD LAYOUT ALL 800 900 MHZ ...
Page 173: ...Revised January 1995 Part No 001 9750 003 10 16 RF BOARD BOARD SCHEMATIC 900 MHZ ...
Page 174: ...Revised January 1995 Part No 001 9750 003 10 17 RF BOARD BOARD SCHEMATIC UNREVISED 800 MHZ ...
Page 178: ...Revised January 1995 Part No 001 9750 003 10 21 PA BOARD SCHEMATIC 900 MHZ 30W ...
Page 179: ...Revised January 1995 Part No 001 9750 003 10 22 PA BOARD SCHEMATIC 900 MHZ 15W ...
Page 181: ...Revised January 1995 Part No 001 9750 003 10 24 PA BOARD SCHEMATIC UNREVISED 800 MHZ 35W ...
Page 182: ...Revised January 1995 Part No 001 9750 003 10 25 PA BOARD SCHEMATIC UNREVISED 800 MHZ 15W ...
Page 183: ...Revised January 1995 Part No 001 9750 003 10 26 AUDIO LOGIC BOARD SCHEMATIC PART 1 OF 2 ...
Page 184: ...Revised January 1995 Part No 001 9750 003 10 27 AUDIO LOGIC BOARD SCHEMATIC PART 2 OF 2 ...
Page 185: ...Revised January 1995 Part No 001 9750 003 10 28 AUDIO LOGIC BOARD LAYOUT TOP VIEW ...
Page 186: ...Revised January 1995 Part No 001 9750 003 10 29 AUDIO LOGIC BOARD LAYOUT BOTTOM VIEW ...
Page 188: ...Revised January 1995 Part No 001 9750 003 10 31 REMOTE TRANSCEIVER INTERCONNECT SCHEMATIC ...
Page 189: ...Revised January 1995 Part No 001 9750 003 10 32 REMOTE CONTROL UNIT INTERFACE BOARD SCHEMATIC ...
Page 216: ...Part Number 001 9750 007 12 00 hph Printed in U S A ...
