Arrangement having several functional units

A programmable controller comprising an arrangement including:

• (a) a system bus having data and control lines, said data and control lines comprising a bus request line, a bus grant line and a bus lock line;
• (b) a plurality of address lines;
• (c) a plurality of card slots interconnected by said system bus and by said address lines;
• (d) a code generator for generating a card slot code for each of said plurality of card slots;
• and
• (e) a plurality of functional units adapted to be plugged into said card slots, wherein each of said plurality of functional units includes:
• (i) means for determining a card slot code corresponding to a card slot into which a read/write functional unit is plugged, and
• (ii) an arbiter for managing said system bus, with said arbiter capable of being activated according to a selection code;
• with at least two of said functional units comprising read/write functional units, wherein each of said read/write functional units includes:
• (i) a connector for coupling said read/write functional unit to said bus request line, said bus grant line and said bus lock line,
• (ii) means for determining a position code corresponding to a relative position of said read/write functional unit within the arrangement using said card slot codes associated with said plurality of functional units, and
• (iii) means for activating said arbiter when said position code corresponds to said selection code, said arbiter active during operation of the arrangement.

A plug-in functional unit capable of executing a read/write operation, said plug-in functional unit comprising:

• (a) means for determining a card slot code corresponding to each of a plurality of card slots of an arrangement into which functional units capable of executing a read/write operation are plugged, wherein said card slots are interconnected by a system bus having data and control lines, and by a plurality of address lines;
• (b) an arbiter for managing said system bus, said arbiter capable of being activated based on a selection code;
• (c) means for connecting said plug-in functional unit to a bus request line, a bus grant line and a bus lock line of said arrangement;
• (d) means for determining a position code corresponding to a relative position of said plug-in functional unit within said arrangement using said card slot codes;
• and
• (e) means for activating said arbiter when said position code corresponds to said selection code, wherein said arbiter remains active during operation of said arrangement.