· MODES OF SWITCH

1. Switching.

The MT8980/81 provides nonblocking switching of information channels (circuit switching). The main difference between the MT8980 and the MT8981 is that the MT8980 has a 256 channel capacity and the MT8981 has a 128 channel capacity. Each channel has a throughput capacity of 64 kbit/s. Channels may carry any form of digitized signal, from encoded voice or data to digitized video. The MT8980/81 can provide a communication path between any pair of nodes connected to the MT8980/81 through ST-BUS streams. As well, the MT8980/81 can place its ST-BUS outputs into a high impedance state on a per channel basis, so that larger matrices may be constructed.

2. ST-BUS Device Control.

When the MT8980/81 is in Message mode, each ST-BUS channel input

or output looks like a parallel register to the controlling microprocessor. Each of these input

channels or output channels can map directly into the status register, or the control register of

a “remote” ST-BUS device connected to the MT8980/81. An individual MT8980 can read up

to 256 status registers and write up to 256 control registers.

3. Interprocessor Communication.

The ability to provide communication paths between microprocessors is a subset of the previous

application. In this case, the remote ST-BUS device is another MT8980/81 which is controlled

by another microprocessor. This microprocessor is also sending and receiving information on STBUS channels in Message mode. The channel that the remote microprocessor is receiving on

appears to the “local” microprocessor as a control register of an ST-BUS device appeared in

the previous application. The channel that the remote microprocessor is sending on appears to

the local microprocessor as a status register of an ST-BUS device appeared in the previous

application.