RFL 9300 RFL Electronics Inc.
May 1, 1998 14 - 5 (973) 334-3100
In the three-terminal configuration (two RFL 93B CC modules and two RFL 93B MO modules), the TX control line
and the standby lines are pulled low by connecting lines in the RFL 93B CC module placed in CC Slot 2. When
both TX control and the STANDBY lines are low, both RFL 93B MO modules get TX DATA and give RX DATA and
clocks from their respective RFL 93B CC modules. The RFL 93B CC module in CC Slot 1 talks only to the RFL 93B
MO in Modem Slot 1, and the RFL 93B CC module in CC Slot 2 only talks to the RFL 93B MO module in Modem
Slot 2.
Solid-State Heater Circuit. Transistor Q1 is normally biased off if the temperature sensed by thermistor R5 is
greater than +20
o
C. As the temperature falls below +10
o
C, Q1 turns on and acts like a current source that draws
up to 500 mA from the +15-volt supply line. The resultant 7.5 watts is dissipated in resistor R6 and the heat sink for
Q1. This heat sink is located below the plug-on modem card, and keeps its ambient temperature above its speci-
fied minimum (0
o
C.) Resistor R27 limits the current through R5 and prevents thermal runaway as the R5's resis-
tance decreases with temperature. Transistor Q2 is normally off unless the -15-volt supply fails. If the -15-volt sup-
ply fails, Q2 turns on; this turns off Q1 and prevents the heater from coming on unless all supplies are present.
14.3.3 INITIALIZATION
When the RFL 9300 is initialized, the RFL 93B CC module sends commands over the modem bus. These com-
mands reset the RFL 93B MO and configure it for 7.2-Kbps operation. The RFL 93B MO must receive a "training
sequence" from the remote modem before received analog signals can be converted into digital signals. When the
RFL 93B MO modem module gets the commands for reset and configuration, the final phase of this operation
sends a training sequence to the remote modem. The RFL 93B CC module gives a message to the modem which
requests a training sequence from the remote terminal. The remote modem should be receiving messages and the
remote RFL 93B CC module decodes the training sequence request signal. The RFL 93B CC module at the remote
terminal then commands the remote RFL 93B MO module to send a training sequence and communications are
now established in both directions.
The messages sent over the control bus between RFL 93B CC and RFL 93B MO modules are arbitrated by the
RFL 93B SV supervisor module. In a three-terminal configuration, two RFL 93B CC modules must talk over the
same bus to two RFL 93B MO modules. Contention is avoided because the RFL 93B CC module in Slot 1 sends
one step in the initialization sequence, and then gives control over to RFL 93B CC module in Slot 2 by lowering the
/COM2 address line. The RFL 93B CC module in Slot 2 then sends the next step in its initialization sequence to the
RFL 93B MO module in Slot 2. If too much time has passed, the RFL 93B SV raises all the /COM address lines and
the procedure is tried again at the next 0.5-ms system tick from the RFL 93B SV. The result is a 0.5-ms delay be-
tween each step in the initialization sequence; this delay gives the RFL 93B MO a chance to react to the control
commands (especially the reset command).
The messages sent from the RFL 93B CC module on initialization are as follows:
Step Address Bits Set Bits Cleared Comments
1 00000000 00000000 00000000 /RESET line low
2 10000000 00000000 00000000 /RESET line high
(If sending training only, start here.)
3 10100111 00000010 00000000 Set T/2 bit
4 10000111 00000000 10000010 Clear RTS and X CLOCK
5 10000110 00010010 00000000 Set TX for 7.2 Kbps
6 10100110 00010010 00000000 Set RX for 7.2 Kbps
7 10101110 00001000 00000000 RX SET bit ON
8 10001110 00001000 00000000 TX SET bit ON
9 10000111 10000000 00000000 RTS ON (send train)
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