1.3 General Description

The BI-0433 12 Channel Incremental Encoder Interface module is a VMEbus slave module. The module decodes the address lines A1 to A15 and responds when receiving the address modifier codes $29 and/or $2D (short supervisory/non-privileged I/O access). The module appears to the system as 256 byte locations which can be placed on any 256 byte boundary in the 64 kbyte short I/O space.

The module consists of 12 input channels with four differential inputs each. The channels are grouped in four independent groups. Each group is based upon two CF32006 triple incremental encoder counters and has its own synchronization and control logic.

The differential inputs are optically isolated from the synchronization circuitry. An isolation of 500 V is maintained between any two inputs and between any input and the system.

Each channel has two quadrature input signals, one index input and one digital input. The index input may reset the corresponding counter and/or generate an interrupt. The polarity of the index input is programmable.

The index and the digital input create a two bit digital input channel. A change of a digital input line of a channel can be detected and may generate an interrupt when this change is detected. The interrupter is a MC68153 Bus Interrupter Module (BIM) which has a software programmable interrupt level, interrupt vector and interrupt mask register for each of the four channel groups.

The differential input signals are continuously monitored to check whether a proper differential signal is applied to the inputs. When a non-differential signal is detected, due to missing connections or electrical shorts, cable fault bits are set in registers which can result in an interrupt to the VMEbus being asserted.