Technical data

Features
8-15
8
Features
Signal Line Termination
To prevent signal reflections, most signal lines not autojumpered
are terminated with 470-ohm (pull down) and 330-ohm (pull up)
resistors (a few lines have specialized terminators, depending on
the nature of the signals they carry). These resistors are arranged in
networks. They are permanently installed on the front of the
backplane. For J1, the networks are located at opposite ends of the
backplane adjacent to the first and last upper row (J1) connectors.
For J2, the networks are located at opposite ends of the backplane
adjacent to the first and last lower row (J2) connectors.
In addition to the VME specification termination noted above,
selected signals on some backplane boards have additional signal-
enhancing components (such as on the DTACK and BERR bus
lines).
Autojumpering
For propagation of the Bus Grant and Interrupt Acknowledge
daisy-chain signals, VMEbus protocol requires that all empty slots
(and all slots containing VMEmodules whose artwork does not
provide for propagation of the daisy-chain) have a means of
shorting daisy-chain inputs to outputs at the connector socket.
In many VME backplanes, the daisy-chain lines of the VMEbus are
manually shorted with removable jumpers. However, the
Exchange Ready chassis backplanes have an autojumpering feature
that detects unoccupied connector sockets and determines whether
the VMEmodules installed are capable of daisy-chain signal
propagation. If the slot is unoccupied, or if the signal is not passed
on via the VMEmodule, the signal is propogated through a buffer
on the backplane.