AR# 1501: Foundation: Connecting a symbol bus pin to a bus of different width
AR# 1501
Foundation: Connecting a symbol bus pin to a bus of different width
Description
Keywords: Foundation, Bus Pin, Connections
Urgency: Standard
General Description: On a Foundation schematic, if a 16-bit bus BUS[15:0] is connected to an 8-bit symbol pin PIN[7:0], then by default the MSB of each bus will be connected, proceeding down (BUS15 to PIN7, BUS14 to PIN6, etc.) The lower bits of BUS will not be connected to the symbol.
Similarly, if an 8-bit bus BUS[7:0] is connected to a 16-bit symbol pin PIN[15:0] the connections would be BUS7 to PIN15, BUS6 to PIN14, etc. The lower bits of PIN will not be connected to the bus.
How can the connection between the bus and the pin be controlled?
Solution
Double-click on the end of the symbol's bus pin, and you will get a dialog box titled "Bus pin connections". Type into the description field the order you wish the connections to be made, from MSB to LSB of the symbol's bus pin.
For example, suppose you have an 8 bit bus BUS[7:0] and a bus pin PIN[15:0], and you want to map BUS6 to PIN15, BUS7 to PIN14, and then BUS[5:0] to PIN[13:8] (leaving PIN[7:0] unconnected). You would enter: BUS6, BUS7, BUS[5:0].
Suppose you now want to map BUS0 go to PIN0, BUS1 to PIN1, etc. Since the width of the bus is smaller than the width of the bus pin, you will need to create a dummy signal or bus, because the Bus Pin Connections dialog will connect signals starting with the MSB.
For example, create an unconnected bus called NC[7:0]. Use this bus as the most significant bits: NC[7:0], BUS[7:0]
Refer to the Foundation Help Contents -> Schematic Editor -> Creating Schematics -> Using Buses. Search for Complex Buses for more information.