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  4. AR# 38334: BPI Configuration Interface Needs Data on Every A<0> Cycle - A<0> Must be Connected to LSB of Address Bus

AR# 38334

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BPI Configuration Interface Needs Data on Every A<0> Cycle - A<0> Must be Connected to LSB of Address Bus

Description

The BPI interface in the Xilinx FPGA devices expects data on every CCLK cycle. This can lead to potential problems when using a standard 16-bit BPI interface. Note that you must always connect an A<0> to the flash addresses.

Solution

A general 16-bit BPI interface does not use the A<0> pin to address the flash memory. This allows forword addressing instead of byte addressing in 16-bit mode. If you use word addressing,it conflicts with the FPGA BPI configuration interface.

The FPGA BPI interface requires data on every CCLK cycle, and, therefore, with every A<0> cycle. If A<0> is not connected and A<1> is the least significant bit of the address bus,each word will be read twice.

The next table illustrates this point:


CCLK

cycle
FPGA

Address bus

Output

FPGA_A[20:0]
Flash

Address bus

Input

Flash_A[19:0]

(FPGA_A[20:1])
Flash returns

the following

data (bitstream)

word

0
21'b00...0000

20'b00...000
Data word[0]

1
21'b00...0001

20'b00...000
Data word[0]

2
21'b00...0010

20'b00...001
Data word[1]

3
21'b00...0011

20'b00...001
Data word[1]

...

...

...

...

This is why A<0> must always be connected to theleast significant bitof the data bus.
AR# 38334
Date 12/15/2012
Status Active
Type General Article
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