UM0434 datasheet(341/390 Pages) STMICROELECTRONICS

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Nexus3 module

UM0434

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Table 229 details the status bit encodings.

12.4.6

Read/Write access data register (RWD)

The read/write access data register, shown in

Table 230, provides the data to/from system

bus memory-mapped locations when initiating a read or a write access.

Table 228.

RWCS field descriptions

Bits

Name

Description

Access control

0 End access

1 Start access

Read/write select

0 Read access

1 Write access

29–27

Word size

000 8-bit (byte)

001 16-bit (half-word)

010 32-bit (word)

011 64-bit (double word—only in burst mode)

100–111 Reserved (default to word)

26–24

MAP

MAP select

000 Primary memory map

001–111 Reserved

23–22

Read/write access priority

00 Lowest access priority

01 Reserved (default to lowest priority)

10 Reserved (default to lowest priority)

11 Highest access priority

21–16

—

Reserved

15–2

CNT

Access control count. Number of accesses of word size SZ

ERR

Read/write access error. See

Table 229.

Read/write access data valid. See

Table 229.

Read/Write access status bit encodings

Read action

Write action

ERR

Read access has not completed.

Write access completed without error

Read access error has occurred.

Write access error has occurred

Read access completed without error

Write access has not completed

Not allowed

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