Lexicon
7-7
At startup, the system software polls each slot to detect the presence of an IO card. When no card is
present in a slot, a default DATA bus value of 0xFF is provided by pullup resistors, R11-R14, and R24-R28
to signify this condition.
Clock Terminations
Passive termination networks (R40/R41/R45, R38/R39/R44, R36/R37/R43, R33/R34/R42, R2/R3/R1) are
used on the local clock signals (IOBUS_256FS, IOBUS_128FS, IOBUS_64FS, and IOBUS_FS to manage
signal reflections and levels. Currently, none of these local FS related clocks are used by any IO card.
Sheet 2
Power
Power is provided to the IO card in two ways. The +5v, +12v rails come directly from the 960L power supply
via connector, J9. The –12v rail is supplied by the NLX backplane via connectors J11 (sheet 1).
MIDI
The MIDI interface signals come from a MIDI card located on the NLX backplane. Signals are carried over a
15 pin ribbon cable to connector, J8.
RS232
The two RS232 ports on the PC motherboard are connected to the IO backplane using 10-pin ribbon
cables. COM Port 1 connects connector J6 and COM Port 2 connects to connector J7.
Miscellaneous
The serial audio data signals, TMIX1_SERD* and TMIX2_SERD* are pulled up by resistors, R4-R10, R17-
R23. Capacitors, C2, C11 are bypass capacitors.
I/O Clock card - Input/Output and Clock Generator card
The I/O Clock card provides external interfaces and clock generation for the digital audio subsystems.
Interfaces for midi control and external wordclock sync are supported, along with ports for the LARC2
remote control for the 960L. Clocks can be derived from internal crystal timebases or from external sources
via an on-board Phase-Locked Loop (PLL). The supported sampling rates are 44.1 or 48kHz in single-
speed mode or 88.2/96kHz in double-speed mode.
Midi Interface
On-board signal-conditioning circuitry interfaces external midi current-loop signals with internal logic levels,
which connect to a midi adapter card located in slot 3 (bottom slot) of the NLX backplane. Midi input on J3
(MIDI INPUT) is current-limited by R18 and optically-coupled by U11 (HCPL0601), which converts it to 5V
logic level MIDI_RXD (high=marking, low=spacing). Midi input is echoed directly, without decoding delay, to
J5 (MIDI THRU) via inverter U12 and current-driver transistor Q2 (2N3904), with R23 and R24 providing
current limiting. MIDI_RXD connects to the IO backplane, which in turn feeds it to the midi adapter, which
contains the asynchronous serial receiver that interfaces the serial data to the NLX motherboard. Midi
transmission originates on the midi adapter and arrives on the IO backplane as logic level MIDI_TXD
(high=marking). Inverter U12 and transistor Q1 drive J4 (MIDI OUTPUT), with R20 and R21 providing
current limiting.
Ttl Wordclock Interface
An external TTL-level wordclock-rate squarewave applied to BNC connector J6 (or J7) can be used as a
reference for synchronizing the internal sample rate. The input automatically configures itself as either a 75-
ohm termination or as a high-impedance bridging loop. Each connector contains an internally-switched 75-
ohm terminating resistor which disconnects when an external mating BNC connector is present. With just
one BNC cable connected, the resistor in the other connector terminates the line. With two BNC cables
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