RFL Electronics RFL 9300 - Page 269

RFL 9300 RFL Electronics Inc.
August 9, 2001 9 - 8 (973) 334-3100
JUMPERS
101 Enables or disables the IRIG-B demodulator section (leave in the “in” position for modu-
lated IRIG-B signals).
J102 Enables or disables the IRIG-B demodulator section (leave in the “in” position for modu-
lated IRIG-B signals).
J103 Enables or disables the IRIG-B demodulator section (leave in the “in” position for modu-
lated IRIG-B signals).
J104 Enables or disables the watchdog timer (leave in the “norm” position for normal operation).
J105 Selects the size of the EPROM to be used (leave in the factory selected position).
9.3.3 THEORY OF OPERATION
For the following discussion refer to Figure 9-7, sheets 1 and 2.
MICROCONTROLLER
The heart of the oscillography board is U125, an 80C320 8-bit microcontroller. It runs a program stored in
EPROM U116. It has access to the battery backed, non volatile RAM, U117. The microcontroller is monitored by
a microcontroller supervisor circuit, U115. This circuit contains power up circuitry and a watchdog timer. The
controller timing is crystal controlled by Y101.
PROGRAMMABLE LOGIC
An ACTEL FPGA (field programmable gate array) provides the logic for many of the functions of the oscillogra-
phy board. It forms registers which can be written to by the controller. It also decodes the addresses for the reg-
isters and external hardware registers. The ACTEL, U124, also provides control signals to the bidirectional data
bus with the display controller. It allows the processor to read the state of the trip and current sense signals for
display and recording purposes.
U109 is a programmable logic device that contains AND gates and fixed OR gates. It will latch the AUX TRIP
and LOR TRIP signals active, even when the input trip or DTT signal disappears.
DISPLAY CONTROLLER COMMUNICATIONS
The oscillography board acts as a slave and responds to transmission requests from the Display Controller
board. (Refer to the section “Oscillography Board Communications” above for more details.) The receive flag is
generated inside the Actel chip, along with most of the control signals. Inverter U120 is used to buffer the sig-
nals.
IRIG-B RECEIVER
The oscillography board also contains a circuit to demodulate the IRIG-B signal from an amplitude modulated
1Khz carrier. This circuit is made up of transformer T101, U108, U112, and U113. If jumpers J101, J102 and
J103 are in the “in” position, this circuit strips off the carrier and leaves a digital representation of the IRIG-B
signal. If the jumpers are in the “out” position, the signal is passed to the processor without demodulation. This
is used when an unmodulated signal is supplied to the RFL 9300.
TRIP SIGNALS
Optoisolators, U101-U105 are used to electrically isolate the trip and DTT input signals from the logic circuits.