Service manual

(c) T8
T8s are also 32 bit processors but have floating-point co-processors. They are used for
more computationally intensive tasks, in particular the calculation of all coefficients for DSP
work (fader position, EQ, filters etc.). This is carried out in real time, unlike some systems
which use look-up tables. This has the advantage of allowing continuously variable
functions, rather than steps. T8s are provided with 4M byte of on-card memory.
The T8 then is used to generate the coefficients and manage the card, but actual signal
processing is carried out by the dedicated micro-programmed DSP chips which are
specifically designed for the processing of audio and implement multiple hardware paths.
Control Topology
The transputers in the system are linked together into a hierarchical tree structure. The
convention is that a link 0 is an “up” link, with links 1, 2 and 3 used as “down” links. The link
topology drawings show the structure with the TranSCSI card at the top of the tree, with
sub-systems fanning out beneath it. The parent-child relationship is determined by the
services connections once the system is booted, any configuration of communication paths
can be set up by the software.
Link 3 is seldom used: this is because where possible it is reserved for use as a software
diagnostic port.
Links are sent differentially between cards at RS485 levels. It is essential that they are
correctly terminated if unused so that noise is not interpreted as valid program data during
bootup.
Each processor in a network may be reset by a parent and provide individually-controlled
resets to three children. Errors occurring on any child may be detected by its parent. The
Analyze control line enables the network of transputers to be halted and its state examined
by the development system. Diagnostic LEDs are provided on all boards to show transputer
activity and are laid out in a standard form:
Red Transputer Error
Green Link 0 Output Activity
Green Link 1 Output Activity
Green Link 2 Output Activity
Green Link 3 Output Activity
Red Reset
Some cards also have six yellow software-controlled LEDs that give further status
information.
Digital Service Manual
Issue 3 Page 5