The correlator is made of 8 fully independent units, connected to the IF system through a software configurable distribution system. Each unit processes 6 antennas and 15 baselines. The 8 units are totally independent from each other.
Each unit is divided into three parts: the IF processor, controlled by a simple micro-controller (IF-micro), the master digital processor, controlled by a 68040 microprocessor, and the satellite digital processor, controlled by a 68030 microprocessor. The ``master'' crate contains all samplers, the main control board, correlator board, and a high speed (1 Gbit) serial link emitter to transmit the samples to the ``satellite'' crate. The ``satellite'' crate contain a high speed receiver, and correlator board to process the remaining correlations.
The ``master'' micros communicate to the IF-micro through a serial link. All 68xxx processors are linked to the main acquisition computer of the PdBI by a dedicated Ethernet link. The IF-micro controls all the low-level functions required in the analog part: frequency setting, low-pass filter selection, oscillator phase control (value and rate). The ``master'' microprocessors control all the digital parts: multiplex factor, delay steps, correlator board readout, Fast Fourier Transform, small delay correction, bandpass correction, frequency and time averaging, etc... The ``satellite'' micros do not handle any IF or sampling operation: only correlator board readout and subsequent calculations are performed here.