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# AR# 1501

## 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