Communications bus and controller

A communications system, comprising:

• a framed, time-division-multiplexed, synchronous bus, having:
• an information channel on which communication in a first mode and communication in a second mode can be selectively effected;
• and
• an allocate channel;
• said information channel having a bandwidth and being pre-allocated for communication in said second mode, and said allocate channel having asserted thereon an allocated signal if said bandwidth of said information channel is being used for communication in said second mode;
• and
• a controller coupled to the framed, time-division-multiplexed, synchronous bus, wherein said controller is a state machine switchable between states corresponding respectively to said first and second modes of communication on said bus, and said controller is responsive to said allocated signal to inhibit communication in said first mode using said bandwidth of said information channel when said allocated signal is not asserted;
• and
• a store storing a foreground template and a background template, said controller having a read and/or write access status in respect of each slot of each frame and said foreground template defining said access status for each said slot, and a means for swapping said foreground template for said background template in response to a swap signal on said bus.

A communication system comprising:

• a framed, time-division-multiplexed bus;
• a plurality of communications controllers;
• and
• a corresponding plurality of engines, each one of said engines being coupled to said bus by means of a corresponding one of said communications controllers for controlling the writing of signals to the bus from said engine and the reading of signals from the bus to said engine,
• said bus having an information channel on which communication in a first mode and a second mode can be selectively effected, and an allocate channel on which one of said communications controllers can assert an allocated signal;
• and each one of said communications controllers being a state machine switchable between a first state corresponding to said first mode of communication on said bus and a second state corresponding to said second mode of communication on said bus;
• in which said information channel is pre-allocated for communication in said second mode and in which communication in said first mode on said information channel can be inhibited to allow communication in said second mode on said information channel, said one of said communications controllers, on transmitting, or writing, to said bus in said second mode on said information channel, asserting an allocated signal on said allocate channel to signal to others of said communications controllers on said bus the inhibition of communication in said first mode on said information channel.