M. Braking/Steering Control Unit (BSCU) The BSCU is installed in a 6MCU-size case in rack 90VU (Shelf 94VU). Its functions are:
 -
Braking control through the servovalves and the pressure transducers,

 -
Braking regulation through the check of the speed of each braked wheel,

 -Integrated monitoring with memorization of the failures which come from the different LRUs of the system. It permits to locate the failures during maintenance operations, from the CFDS.
 -Automatic braking control via a braking order. The braking order is servoed to control the A/C acceleration rate according to a predetermined deceleration rate.
 -Nosewheel steering control through a hydraulic block and an actuating cylinder (Ref. 32-50),
 -Conversion into ARINC 429 data of the brake temperatures which come from the Brake Temperature Monitoring Units (BTMU) attached to the main landing gear.
 All the functions use the digital technology.
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 (1) Description of the BSCU
 (Ref. Fig. 027)
 The BSCU has:
 -Two power supply units (one for each system)
 -An ARINC 600 connector at the back (Size 2, 400 contacts).
 -A rear interface with a specific cover to protect the unit against EMI.
 -Six electronic boards The dimensions of these boards are 225 x 175 mm. They are installed vertically and lengthwise in the case. They are connected together and to the rear interface by means of two connectors that occupy the totality of their backplanes. There are two identical sets of three boards that form the systems 1 and 2: two Input/Output boards and one CPU board. Each board with a CPU is connected to an On-Board Reprogrammable Module (OBRM) that includes PROMs.
 The layout of the boards in the BSCU is shown in the referenced figure.
 (Ref. Fig. 028)
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 BSCU
 Figure 027
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 BSCU - Internal Architecture
 Figure 028

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 (2) Description of the systems 1 and 2 Each system is supplied independently with 115V 400 Hz power and has two channels. Each channel has its own power supply (+ 5V, plus or minus 15V) and acquisition modules. A control channel ensures the slaving functions and produces the currents which are sent to the electro-hydraulic components. A monitoring channel dialogues with the control channel through a serial link and monitors the control channel.
 (a) Control channel This channel uses two boards: the CPU board and the I/O1 board
 1 CPU board
_ (Ref. Fig. 029) This board executes all the functional programs. It is built around an INTEL 80486 microprocessor that operates at 32Mhz. This board has:
 -
a 4 Mbyte flash memory (OBRM)

 -
a 256 Kbyte RAM

 -
a 64 Kbyte EEPROM (dedicated to the BITE) The CPU board ensures:

 -DSI (discrete inputs) acquisitions,
 -DSO (discrete outputs) generations,
 -DGO (digital outputs) generations,
 -Relays controls,
 -RS232 link with Automatic Test Equipment (ATE),
 -Link with I/O1 and I/O2 boards
 -BITE functions
 2 I/O1 board
_ (Ref. Fig. 030) This board perform the analog and digital (ARINC) acquisition. It generates analog output and dialogs with the CPU board via a common RAM located on the CPU board. This board is built around a DSP TMS 320C31 microprocessor that Operates at 40Mhz. This board has:
 -
a 1 Mbyte flash EPROM

 -
a 512 Kbyte RAM
 The I/O1 board ensures:

 -ANI (analog inputs) acquisitions,
 -DGI (digital inputs) acquisitions,
 -ANO (analog outputs) generations,
 -Power supply (5V plus or minus 15V) monitoring
 -Switching controls.
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 BSCU - Control Channel - CPU card
 Figure 029

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 BSCU - Control Channel - I/01 card
 Figure 030

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 (b)
 Monitoring channel (Ref. Fig. 031) This channel uses a single board: the I/O2 board. This board is built around a DSP TMS320C31 that operates at 40Mhz. It performs all the acquisitions and computations which enables to monitor the control channel. The monitoring function is ensured by the comparison of the computation results with wraparound of the orders sent by the control channel. The monitoring board is connected to the control boards by an interface bus. This board has:
　
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