xcpu09-frontMain Controller Board for NEXUS Base Devices

  • Base Device and routing control and monitoring
  • Control-computer communication via Ethernet, RS 232, RS 422, or USB
  • Synchronisation and clock-generation control
  • Sample rates of up to 96 KHz
  • Stores the current system status independently of the control computer
  • Wordclock I/O, internal clock generator
  • Test tone and noise generator
  • Metering-information gathering
  • Loudness metering and spectrum analysis (option)
  • Temperature monitoring

 data sheet (124 kb)

The XCPU board is the main controller of NEXUS Base Devices and is pri­marily designed for controlling the routing, including redundant lines. It also handles the communication with an external control com­put­er, sys­tem management, and controls and monitors all system com­po­nents including power-supply units and backplanes. The external con­trol computer providing the graphical user interface is connected via an RS 232/422 or USB port. The changeover to the USB port occurs au­to­mat­i­cal­ly.
The XCPU 09 now features an Ethernet port simplifying integration into existing computer networks.
The USB port can now be used in parallel with the RS 232/422 interface. (The previous XCPU versions only allowed for either the USB or RS 232/422 formats to be used at one time.) A total of three RS 232/422 ports are available: one onboard interface plus two extra ports on the optional XDEM expansion. You select the RS format (RS 232 or RS 422) using a quadruple jumper.
The XCPU 09 includes an exceptionally powerful processor providing sub­stan­tial­ly more power than its predecessors. Therefore, the board can now perform extra tasks which used to be handled by external per­iph­erals.
The XCPU 09 implements two critical new functions as optional modules: EBU-R 128 compliant loudness metering and spectrum analysis. (Refer to the specifications sheet for details.)


The XCPU board supports internally generated or externally refer­enced standard sample rates (44.1, 48, 88.2, or 96 kHz; other rates can be implemented on request). Synchronisation and clock generation are achieved using a PLL with an extended time constant for a low-jitter sys­tem clock.

The system provides the following sync modes:

  • Internal sync — The generated wordclock is output via a BNC port for use as studio master clock.
  • Synchronisation to an external wordclock. The board features a dedicated port for this purpose.
  • Synchronisation to any digital port or to a fibre-optic line.
  • Video-burst sync. Requires an optional XSYNC interface board.

Multiple sync sources can be set up. In the event of a sync source failure these sources are automatically selected according to a user-programmed priority list.

Test Tone Generator

The XCPU comprises a precision digital test tone generator with ad­just­able rate and level. In addition, the generator can produce white and pink noise. The digital audio signals are produced by a DSP. A D/A con­vert­er incorporated on the board makes the signal available in an an­a­logue format.


The board provides a peak-metering function that uses a DSP to detect the data of all 256 time slots and transfers this to the connected PC for viewing purposes.


The XCPU-board firmware is stored in flash memory and can therefore be updated using a service program running on the PC.
All volatile data is stored to a battery-backed SRAM. This ensures the most recent Base Device and system statuses are restored after pow­er failure or shutdown. The SRAM is backed-up by a conventional user-­replaceable lithium battery. The system displays a message when the battery needs replacement.
The XCPU also provides a micro-SD slot for future expansion.

Board ID

All Base Devices on the NEXUS audio network feature unique IDs. The IDs are selected using encoder switches on the physical XCPU board.

XCPU09 Specifications

CPU Type Motorola MCF547x
Clock rates Core: 200 MHz, Bus: 50/100 MHz
Working memory 2 Mbyte SRAM, battery-buffered; 64 Mbyte SDRAM
Flash 16 Mbit; 64 Mbit max.
Micro-SD card 32 GB max. (at the time of writing)
RS232 Interface Port Mini DIN, 8-pole, galvanically isolated
Baud rate 38.4 kBaud (typ.), 115.2 kBaud (max.)
Cable length 10 m / 33' (max., recommended)
RS422 Interface,
Port D-Sub terminal (9-pole), galvanically isolated
Baud rate 38.4 kBaud (typ.), 115.2 kBaud (max.)
Input level -7 to 12 V (max.)
I/O impedance 120 Ohm
Cable length 100 m / 330' (max.) @ 110-ohm line (±20%)

USB interface
Type compliant to USB Rev. 1.1, type B; standard pinout; galvanically isolated
Baud rate 12 Mbps, typ. 38.4 KBaud; 115.2 kBaud (max.)
Recommended cable length 5 m / 16.4' (max.) @ 90-ohm line (±15%); 25 m/82' with active extension
Port RJ 45, 10/100 Base TX, galvanic isolation
Data rate 10/100 Mbps
Cable length 100 m max., CAT5e
Wordclock Input
Port BNC, galvanically isolated
Level 1 to 5 V
Impedance 75 / 500 ohm, configurable
Rate 44.1 KHz, 48 KHz, 88.2 KHz, 96 KHz
Required frequency stability min. < ±150 ppm (typ. ±50 ppm; compliant with AES 11, Grade 2)
Wordclock Output
Port BNC, galvanically isolated
Level 2.4 V on 75 Ohm
Rate 44.1 KHz, 48 KHz, 88.2 KHz, 96 KHz
Frequency stability min. ±10 ppm (typ. ±5 ppm, internal oszillator)
Sample rates
Supported default rates 44.1 KHz, 48 KHz, 88.2 KHz, 96 KHz

Test tone Generator
Frequency range 20 to 20,000 Hz, adjustable in 1-Hz steps, white and pink noise
Frequency deviation < 0,01 Hz
Level -34 to +6 dBu in 1-dBu steps
Level deviation ±0.3 dB @ 1 KHz
THD&N. < 0,1%
Type: digital multichannel metering; audio-bus time-slot metering, consideration of the 14 most significant audio bits
Channels 256
Measuring type peak
Resolution 0.25 dB
Retrace 20 dB / 1.5 s

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