Ritron DATAFLOW RTU Series Technical Specifications page 9

over a RS-485 serial link. The following paragraphs describe how individual blocks of the control board
operate.
17.1.1 +5V REGULATOR: IC101 is a DC-to-DC converter which changes the VUNREG input voltage to
+5VDC. The +5VDC value is set by resistors R101, R102, and R103 with FB = 2.50V (pin 13). This IC also
contains an output comparator used to monitor system +5VDC voltage. This comparator shuts the system
down if low power is detected to prevent abnormal system operation due to low voltage.
17.1.2 VREG REGULATOR: IC112 is a DC-to-DC converter which changes the VUNREG input voltage to
+8.5VDC. The +8.5VDC value is set by resistors R148 and R149 with ADJ = 1.23V (pin 5). This IC also
contains an ENABLE pin (pin 1) which allows the microprocessor to turn this regulator ON and OFF. With
5V applied to the ENABLE pin, the regulator is ON; with 0V applied to the ENABLE pin, the regulator is
OFF.
17.1.3 4 Hz. INTERRUPT CLOCK: IC102 provides a 4 Hz. clock to the microprocessor, which functions as
an interrupt timer to make the microprocessor read all the digital and analog inputs. The 4 Hz. rate is made
by dividing the 32768 Hz. crystal (Y101). To save power, IC102 is not run at full +5V. Diodes CR103 and
CR104 are used to decrease the supply voltage to IC102.
17.1.4 MICROPROCESSOR. IC105 The microprocessor is a Motorola MC68HC705B16. This 8-bit MCU
contains an on-chip oscillator, CPU, RAM, ROM, EEPROM, A/D converters, pulse length modulated
outputs, I/O, serial communications interface, programmable 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.
17.1.5 DES ENCRYPTION PROCESSOR. IC106 is not placed at this time.
17.1.6 EXTERNAL RAM. IC108 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. Q101 disables writing to the memory when the +5V supply is low. This prevents unwanted data to be
written to the RAM.
17.1.7 PORT EXPANDER. IC109 is a CHMOS programmable peripheral interface. It extends the amount of
I/O 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.
17.1.8 INPUT PROTECTION. The analog inputs are protected against over voltage and negative voltage as
well as being current limited. The circuitry between connector J101 and the processor provides this
protection. This circuitry should not change the incoming signal.
17.1.9 OUTPUT CONVERSION. 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.
17.1.10 SERIAL CONVERTER. IC110 converts the logic level signals of the microprocessor to RS-485
compatible signals. The devices between this chip and connector J105 are for protection only. They protect
the device from over voltage and negative voltage as well as provide current limiting.
17.1.11 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.
17.1.12 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
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