RFL 9300 RFL Electronics Inc.
October 29, 2001 2 - 31 (973) 334-3100
3. All messages passed between controllers at the local RFL 9300 station consist of three bytes: address,
data, and security code. The security code is the XOR of the data and address bytes. All received mes-
sages are tested to insure that the security code is correct. The phase controllers will alarm if the fre-
quency of corrupted messages exceeds 1 in 16.
The RFL 93B SV does not alarm on bad messages received from the phase controllers. It assumes that
if there is a problem receiving messages from the phase controllers, there is also a problem on the
other end and the phase controllers will alarm. Many of the messages passed to the phase controllers,
including programmed variables and CDC values, require an acknowledge sequence. This is the same
three-byte message returned to the RFL 93B SV. The RFL 93B SV will continue to transmit the mes-
sage until the proper acknowledge is received. The parallel port bus test messages between controllers
have deliberately been given the lowest priority. If a given message is continuously being repeated be-
cause a proper acknowledge has not been received the bus test message will never be sent. This will
result in a parallel port bus test alarm (Alarm 34). The same type of error checking exists for all mes-
sages passed between the RFL 93B SV and the display controller board.
4. The 2-kHz system clock generated by the RFL 93B SV is the heartbeat of the system. The accuracy of
this clock is critical because of the differential nature of the RFL 9300 system. Each phase controller
monitors the period of this clock to insure that its period lies between pre-defined limits that are applica-
tion dependent. Since each phase controller will base the test on its on-board crystal, the RFL 9300 has
four independent crystal based frequency discriminators monitoring this clock. If a phase controller de-
tects an error in the clock, it will reset and attempt to re-initialize.
5. The phase controllers and the RFL 93B SV both monitor the CDC values supplied by the Communica-
tions Controller. The maximum value that will be accepted is 31 ms for a 30-bit message pair and 29 ms
for a 15-bit message. If a value exceeding the allowed range is received, the CDC message is not ac-
knowledged. If the condition is not corrected, the transmission of CDC messages will quickly tie up the
local communications channel and cause parallel port alarms.
6. The local 9300 verifies the remote 9300’s transmit address on a periodic basis using a TDM message. It
alternately requests the remote station’s least significant transmit address byte, then its most significant
transmit address byte, at 2.5 second intervals. This will not tie up the communications channel and will
insure some level of protection against any possible undetected switching of the communications link
between stations.
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