ZETRON 2000 Series Specifications download pdf (Page 154)

Theory of Operation

154 025-9035AA

There are a number of jumpers on the SCSI host adapter. These are pre-set at the factory

and should never be changed in the field unless we have given you explicit instructions to

do so.

2200EX

The 2200EX chassis is under control of the 2200 main chassis through its interconnection

via the 702-9204 Expand boards. The Expand boards use high-speed bus transceivers to

interface with each other over a shielded cable. This cable is terminated with a

characteristic impedance that matchs the impedance of the cable. This is done to reduce

signal reflections. The Expand cards can be configured as a Master (2200) or Slave

(2200EX) unit. The direction of each card is determined by the installation of DIP shunts,

which connect the receive outputs of the transceivers, where appropriate.

All applicable PC Bus signals are transmitted from the main chassis and received at the

expansion chassis. These signals include all address lines and the appropriate control lines.

The data bus is bi-directional and can be thought of as an extended wired-or. PC Bus write

data is provided to both the main and slave chassis.

The slave chassis is enabled to drive the data lines back to the main chassis during read

operations only. These lines will not be driven if the slave chassis data bus is inactive. If

the read data is coming from the main chassis, it will drive the main bus directly. The

expansion card data drivers will not interfere since they are open collector.

The PCM data is handled similarly, although it is complicated by the fact that there is no

control signal, such as with the PC read strobes MEMR and IOR, to enable the appropriate

drivers. This lack is overcome by an interlock signal. When one side of the PCM bus starts

to drive low, the transmitted signal blocks the other side from driving back. When the

signal goes inactive, a delayed counterpart of the transmitted signal is used to block

backward transmission for an interval sufficient to prevent unwanted oscillation.

Dual Trunk Card (702-9117) Rev D and Later

The Dual Trunk Card interfaces two sets of telephone lines to the paging terminal.

Telephone lines are brought to the Dual Trunk Card through the Z-bus. Which lines are

brought to the Dual Trunk Card is dependent on the slot the Dual Trunk Card resides in.

Each slot has access to two separate unique telephone lines.

The Dual Trunk Card can interface different types of lines. Dual four position matrix

plugs determine the type of interface provided for each trunk. The two trunks need not be

set to the same line type. In the DID position, the interface is for C.O. Selector level, local

or PABX loop-start trunks. The E-E position is for End-to-End operation, usually as a

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ZETRON 2000 Series Specifications Page 154