RFL 9300 RFL Electronics Inc.
August 9, 2001 9 - 4 (973) 334-3100
9.2.3 THEORY OF OPERATION
For the following discussion refer to Figure 9-7, sheets 4 and 5.
MICROCONTROLLER
The heart of the display controller is 16-bit microcontroller U309. The 80C196KD microcontroller U309 has 1024
bytes of internal RAM, and operates with a 16-MHz crystal. It also contains a serial port, 48 I/O lines and two 16-bit
timer/counters. The program and data for U309 are stored in EPROM's U314 and U315. Jumper J302 is set ac-
cording to the type of devices installed for U314 and U315. J302 is placed in Position A for 27C256 devices, and in
position B for 27C512 devices. When 27C512 devices are used, the most significant address line is controlled by
microcontroller U309, allowing it to bank switch the program memory. U312 and 313 are used to latch the address
bus using the ALE signal from the microcontroller. External data is stored in a 2Kx8 RAM chip (U311). Address de-
coding for the peripheral devices is accomplished in programmable logic chip U305. Data to and from these de-
vices is buffered by U316 and U317, respectively.
MICROCONTROLLER SUPERVISOR
Microcontroller supervisor U308 contains a watchdog timer. Its output (U308-7) is normally high. About once every
2 ms, microcontroller U309 pulses its I/O port 1.0 output (U309-19) several times. This keeps the watchdog timer
from timing out and causing U308-5 to go low. If, for some reason, the watchdog timer does time out, U309 is reset
and begins its program again. During the reset, the communications control buffer U304 and two gates of quad
buffer/line driver U301 are disabled by U318-6. This prevents any false signals during startup.
RS-232 COMMUNICATIONS
The /BACK UP EN, /CTS, /DCE, and /SC_RDY signals from the RFL 93A SV Supervisor Module and the RS-232
bus are entered through octal buffer U304, and are fed to U309's I/O port 0. The RS-232 TX is only enabled when
U309-10 drives the /CTS signal low. /AUX LATCH DIS, /LOR LATCH DIS, /RTS, and /DC_RDY are output signals.
They are derived from U309's I/O port 1, and are transmitted to the Relay I/O or the RFL 93B SV through U304.
RS-485 COMMUNICATIONS
RS-485 communications is provided through RS-485 transceiver U303. U303 has a separate enable for its trans-
mitter and receiver sections. Before U303's transmitter can be active, the /RTS line must be high, driving U302-10
low. In addition, the /SC_RDY line must be low, making U302-4 high. U303's receiver is enabled whenever
/DC_RDY is made low; this means the display controller is able to receive communications from the RFL 93B SV.
Incoming RS-232 signals (/RX DATA) are buffered by U301 and fed to U309's serial input. The /DC_RDY signal
must be high in order to enable the U301 buffer. The 60/50 HZ signal is brought in through NAND gate U318 and
fed to the microcontroller I/O port 2.3 (U309-44). An audible sounder is activated by I/O port 2.6 (U309-33); its drive
signal is buffered by U318.
OSCILLOGRAPHY BOARD COMMUNICATIONS
Communications between the two boards is accomplished over a bi-directional eight-bit data bus (DOSC_0 through
DOSC_7). The display controller board is the master, and therefore controls the data direction. The inverted direc-
tion control signal to the oscillography card appears on pin C24. Communications is initiated by the display control-
ler, which sets the bus direction to transmit and then writes the command data into data latch U324. The transmit
flag register U306 is also set by the write signal, and is output on C26 to tell the oscillography card that data has
been written to the bus. The transmit flag is reset by the oscillography card when the data has been read. The dis-
play controller will then set the bus direction to receive and wait for data from the oscillography card, which will be
indicated by a receive flag signal appearing on pin A25. When this occurs, the microcontroller will read the data
through U323, which will also reset the receive flag signal from the oscillography card by placing a reset signal on
pin A26. The receive process will continue if more than one byte of data was requested.
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