Installation/ Operation
24.1.4 MICROPROCESSOR.
IC105
The microprocessor is a Motorola MC68HC705B 16. This
8-bit MCU contains an on-chip oscillator, CPU, RAM, ROM, EEPROM, ND converters, pulse length
modulated outputs, I/O, serial communications interface, program mable timer system and watchdog. The
processor is running at a speed of 4 MHz. (Y102). The real world inputs are connected to the processor through
PD0 - PD5. PD6 is used to measure VUNREG voltage. Resistors R122 and R123 are used to scale this voltage.
PLMA and PLMB are used to generate the analog outputs.
24.1.5 DES ENCRYPTION PROCESSOR.
IC106
is not placed at this time.
24.1.6 EXTERNALRAM.
ICI08
is a 32,768 word x 8-bit CMOS static random access
memory. This external memory is used to store incoming and outgoing message traffic. This memory is backed
up by capacitor C126. QlOl disables writing to the memory when the +5V supply is low. This prevents
unwanted data to be written to the RAM.
24.1.7 PORT EXPANDER.
IC109
is a CHMOS programmable peripheral interface. It extends
the amount of I/0 the microprocessor can handle. This chip connects the microprocessor to the external
memory, the relay drivers, the serial communications driver, and the RF board controls.
24.1.8 INPUT PROTECTION.
The analog inputs are protected against over voltage and negative
voltage as well as being current limited. The circuitry between connector Jl 01 and the processor provides this
protection. This circuitry should not change the incoming signal.
24.1.9 OUTPUT COl\'VERSION.
PLMA and PLMB are used to generate the analog outputs.
Connected to each output is a two-pole RC filter, used to convert the pulse length modulation into a DC voltage.
This DC voltage is then fed into an operational amplifier (IC114) to add drive capability to the circuit. The
resistors, transistors, and jumpers after the operational amplifier are used to convert the output to either a
voltage or
a
current output.
24. 1.10 SERIAL CONVERTER.
ICllO
converts the logic level signals of the microprocessor to
RS-485 compatible signals. The devices between this chip and connector Jl05 are for protection only. They
protect the device from over voltage and negative voltage as well as provide current limiting.
24.1.11 RELAYS.
The relays used by the
DATAFLOW RTU
are latching relays. This
means each relay has two coils, one to open the relay and one to close the relay. The signal to open or close the
relay is a short duration pulse. After this pulse the relay is "latched" in that state with no further current draw
through the relay coil. This allows reduced current draw by the
DATAFLOW RTU.
This also means that if
power is lost to the unit the relays stay in their last state.
24. 1.12 MODULATION OUTPUT.
The data modulation for the
DATAFLOW RTU
is Bi-Phase M.
This output modulation is produced by the microprocessor (IC105 pin 2) with a logic level amplitude (0 or 5
Volts). Variable resistor R131 is used to scale this output causing the modulation level to be set. The signal is
then passed through a !ow-pass filter (IC107) with a cut-off frequency of 1500 Hz. The purpose of this filter is
to round off the edges of the square wave input.
24.1.13 MODULATION INPUT.
The data modulation for the
DATAFLOW RTU
is Bi-Phase M.
The received data from the RF board is first run through a low-pass filter (IC107) to clean-up the wave. This
signal is squared-up by a comparator (IC107), and is then decoded by a software decoder in the microprocessor.
24.2
See the applicable RITRON DTX manual for the RF board theory of operation. When using the DTX manual in
support of the
DATAFLOW RTU
only the RF portion is valid. Disregard all references to the DTX control
board.
( A-20)
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