VME Slave Interface - Top Level

VME bus Slave Interface
VME Block Diagram

The graphic represents the major signals that are used by a VME Slave interface.
Power and ground signals which are shown, of course would run to any card connected to the backplane.
However the reset line, which is also shown, might not be used by every card in the system.

Home > Interface Buses > Backplane Buses > VME Bus > VME Slave Interface.

For detailed VME [IEEE 1014-1987] design information see; VMEbus description page.
VMEbus P1 signal assignments.
VMEbus P2 signal assignments.
VME Chassis manufacturers.

A VMEbus Slave interface simply monitors the Address and Data bus for Reads or Writes sent to it.
Once a correctly decoded address is received, the Slave will either receive information {for a Write}, or output information onto the Data bus in the case of a Read.
The bus Master continues to control the Data bus during either interface. A Slave interface may also generate Interrupts over any of 7 IRQ lines.
The Interrupts are acknowledged by the bus Controller.
Any number of Slave boards may reside on the VME bus.
Note the slave-interface is not generating any addresses, just receiving them, comparing them the board address.
All 16 bits of the address bus are being used in the comparison, but that may not be necessary for operation.
Note that Address and Data control can be handled by a few simple state-machines either in PLDs or FPGAs.

So that the block diagram does not become to complex, some things are not shown; for example;
A jumper block may be used to bypass IACK through the board, if the board doesn't generate an interrupt.
Or the jumper could be removed if the board does generate an interrupt.
The Bus Grant [BG] lines may also have jumpers to pass the signals.
For example if the board uses BG3, than Bus Grant lines 0 to 2 may be jumpered on the board, so the board is bypassed.
DIP switches might be used to configure the card for different types of operation; for example to set an interrupt vector.
Switches might also be used to set the interrupt level from interrupt-1 to interrupt level 7.
Switches might be used to set the address level of the card or change the data width [16 to an 8 bit card].
Switches could also be used to select the board address, one bank for A24 to A17 and another switch bank for A31 to A24.

Circuit details;
The address lines could be received via a 74AS821 [AM29821] 10 bit bus flip flop.
A [grounded] switch bank which is pulled up via a 1k resistors, connected to a 74F521 magnitude comparator, also connected to the incoming address lines.

PC motherboard

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Modified 1/31/12
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