AMS Neve S - DMX, User Manual, Page: 22 / 33

In each sampling period, the following sequence occurs:
1. Write channel ‘a’ data into RAM.
2. Read channel ‘a’ data from RAM address offset ‘A’, into DAC A.
3. Convert channel ‘b’ / sample channel ‘a’
4. Write channel ‘b’ data into RAM.
5. Read channel ‘b’ data from RAM address offset ‘B’, into DAC B.
6. Convert channel ‘a’ / sample channel ‘b’.
Delays are altered by changing address offsets ‘A’ and ‘B’.
The RAM card address lines are multiplexed, and the current RAM card being accessed is
selected on the baseboard as a result of the four highest address bits from the memory
control board and the channel selected (0=A, 1=B).
Each 256k RAM card is used to retain 262 144 samples of the analogue signal in the
form of 12 bits of amplitude data (mantissa) and two bits of range data (exponent). At the
normal sampling rate of 25µS per sample, this corresponds to a delay of 6.55 Secs.
Apart from the RAM devices themselves, the card provides data highway buffering and
write control enabling when the card is selected.
The digital signal from the RAM is converted back to analogue form on the DAC boards
(2 off: one for channel ‘a’ and one for channel ‘b’). These cards accept the ‘mantissa
and exponent’ digital input, perform shift left operations on the mantissa dependent on
the value of the exponent (multiplication), and reconstitute the original signal by means
of the DAC device on each board. The DAC outputs is buffered and filtered to remove
sampling steps and fed to the baseboard, then to the output controls, the outputs of
which are fed back to the DAC cards where the balanced outputs are generated.
The interface with the pitch changers, the keypad, the display, the storage of preset
values, the ‘Nudge’ button controls, the status LED controls and all parameter
calculations are performed by the microprocessor board. This board holds the 8085
microprocessor, 2kByte of Programmable Read Only Memory (PROM); 2k Bytes of
CMOS RAM with battery back-up and two programmable I/O devices.
The basic back wiring of the unit is accomplished by the use of a mother board or
baseboard. This board contains all the power supplies for the unit together with the
buffer amplifiers and steering logic.
S-DMX User Manual
Page 20 Issue 3