User's Manual

1.3.2.7.1 Facilities CCA Detailed Theory
System1 and System2 +48V power from connector P2-25 and P2-26 are scaled down by resistor networks
RN1 and RN2 for input to the A-D converter as well as diode-OR’D by CR1 and CR2 to create the
facilities +48V supply. This supply (also named LED_PWR) lights the CR24 PWR_OK LED when
transistor Q1 is turned on under software control by U22-19; indicating all monitored power supplies are
within range.
The facilities +48V is fused by F1 and regulated by regulator U1, L1, diode CR3, and C2 to create +5DIG.
Zener CR36, R68, and SCR Q3 protect downstream circuitry in the event of an over-voltage event by
opening fuse F1. Zener CR37 will short to ground and protect the downstream circuitry if the SCR/Fuse-
blowing circuitry fails for any reason.
The +5DIG supply is further filtered and regulated by regulator U2 and capacitors C3 and C4 to create the
+3.3V supply. The +5DIG supply is also input to DC-DC converter PS1 to create -15V and +15V supplies.
The -15V is filtered and regulated by L2, C8, U3, and C9 to realize -12ANA and by C7, U4, and C10 for -
12DIG. The +15V output is filtered and regulated by L3, C12, U5, and C13 to realize +12ANA and by
C11, U6, and C14 for +12DIG.
The facilities +48V also feeds fuse F2 and regulator U7. Switching regulator U7, C15, L4, CR4, CR5, R10,
C17, and R11 combine to convert 48 volts to +24V. Zener CR38, R69, and SCR Q4 protect downstream
circuitry in the event of an over-voltage event by opening fuse F2. Zener CR39 will short to ground and
protect the downstream circuitry if the SCR/Fuse-blowing circuitry fails for any reason.
The ~MRESET signal enters via P1-B16, is filtered by FL1/C19, diode-isolated by CR6, and resets U8
when active. U8 outputs ~RESET, which clears the outputs of on-board latches U22, U23, and U38.
~RESET is also asserted by U8 if the +3.3V supply drops too low after R14 and before U8-2.
The ~TEST signal enters on P2-B8 and will light on-board indicators CR13-CR21, and CR24 when active.
The ~TEST signal will also cause audio to be emitted from speaker SPK1 when active. The ~TEST signal
is transient-voltage-suppression (TVS) protected by CR40.
Asynchronous data and address busses provided by the RMS CCA enter via connector P2 and are pulled-up
by resistor networks RN12 and RN13. The address bus is decoded into sixteen segments by U9 and U10;
ten of which are used by the Facilities CCA.
The ten spare analog inputs (SPARE_ANA1 through SPARE_ANA10) and four spare digital inputs
(SPARE_DIN1 through SPARE_DIN4) enter via connector P1 and are terminated to ground by resistor
network RN3 before connection to analog multiplexers U20 and U21.
The DIALUP/~EXT control signal enters via P1-C26. When this signal is high, buffer/converter U11 is
enabled and RMM_TX_232, RMM_RX_232, RMM_DTR_232, and RMM_DCD_232 signals will pass
through U11 to Dial-up modem U12 to become ~DU_TXDD, ~DU_RXDD, ~DU_DTRD, and
~DU_DCDD. Components R19, R18, CR9, R20, R17, and CR10 convert +5V signal levels to +3.3V
between U11 and U12. Dial-up modem U12 lights indicator CR13 when a RING is received. Dial-up
modem U12 also lights indicators CR14 through CR17 when serial data and control signals are active.
The tip and ring signals from Dial-up modem U12 are TVS-protected and filtered by CR7, FL2 and FL3
before exiting connector P2-B14 and P2-B15. Audio from U12-64 is scaled by R29 and R31 before audio
header JP1-1.
The DED/~RADIO control signal enters via P1-C25. When this signal is high, buffer/converter U13 is
enabled and RADIO_TX_232, RADIO _RX_232, RADIO _DTR_232, and RADIO _DCD_232 signals
will pass through U13 to Dedicated modem U14 to become ~DED_TXDD, ~DED_RXD, ~DED_DTRD,
and ~DED_DCD. Components R22, R24, CR11, R23, R25, and CR12 convert +5V signal levels to +3.3V
between U13 and U14. Dedicated modem U14 lights indicators CR18 through CR21 when serial data and