Honeywell SPZ-8000 Maintenance Manual page 78

Digital automatic flight control system for gulfstream iv
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MAINTENANCE
Honeywell &LJLJ!!%M.
The bus controller executes a bus frame every 25 milliseconds, 40 times a
second. Two short messages from the bus controller begin each frame, a
frame-start message and a control/test message. The frame-start message is
simply a 'wake-up' call announcing to all users that a new frame is starting.
The control/test message is reserved for functions such as identifying the
frame number (O through 7 in this example) and controlling maintenance test
activity. Following the control/test message, the bus controller requests
all users to transmit for that particular frame. Figure 5 illustrates a
typical bus activity during a frame. Following the start and control/test, a
request for IRS 1 is transmitted on both buses. IRS 1 responds with its data
on Bus A.
IRS 2 request is transmitted on both buses.
IRS 2 responds with
data on Bus B. This process continues as in Figure 5 until all subsystems
have transmitted their messages.
Both buses then go inactive until the
beginning of the next bus frame.
The bus controller repetitively transmits user subsystem requests at the
proper times, independent of whether the subsystems actually respond with
their data messages. User subsystems need not all be in existence on the
bus. Requests may be transmitted for subsystems which are optional and not
installed in a particular application. The bus controller database defines
the length of each user message so that the bus controller may request
transmission at the proper times, independent of responses.
The ASCB interconnects for the SPZ-8000 DAFCS with EDS are shown in Figure 6.
Physical characteristics of the ASCB are listed 'below:
. There are two independent ASCBS denoted "An and "B", each consisting of
one wire pair.
. The ASCB transmission lines shall be Ra.vchem2524E0114 with a thermorad
jacket.
Each ASCB transmission line pair shall
125 ohms t 5 ohms. The characteristic
picofarads/foot.
Each ASCB transmission line pair shall
have a characteristic impedance of
capacitance shall be 12 i 2
be terminated at its two ends with
noninductive 127-ohm resistors t 1%, 1/4 watt, metal film. The cable
length between the last stub and the termination resistor shall be 24
inches.
. The ASCB transmission lines shall have a maximum length between
terminators of 150 feet.
c
Stub lengths at each user pickoff shall not exceed 36 inches. Stub
connections to the main bus shall be accomplished with bus couplers as
shown in Volume II, Section 6, InterconnectsTable 501, Figure 3-7.
22-14-00
Page
25
Aug 15/91
Use or disclosure
of reformation
on this page is subpcf
to the restrictions
on the title page of this document,

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