DMA Controller Module Programming Model

 

 

 

Table 16-3. DCRn Field Descriptions (continued)

 

 

 

 

 

 

 

 

 

Bits

Name

 

 

 

Description

 

 

 

 

 

 

 

 

 

27–25

BWC

Bandwidth control. Indicates the number of bytes in a block transfer. When the byte count reaches a multiple

 

 

of the BWC value, the DMA releases the bus. For example, if BCR24BIT is 0, BWC is 001 (512 bytes or value

 

 

of 0x0200), and BCR is 0x1000, the bus is relinquished after BCR values of 0x0E00, 0x0C00, 0x0A00, 0x0800,

 

 

0x0600, 0x0400, and 0x0200. If BCR24BIT is 0, BWC is 110, and BCR is 33000, the bus is released after 232

 

 

bytes because the BCR is at 32768, a multiple of 16384.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Encoding

BCR24BIT = 0

 

BCR24BIT = 1

 

 

 

 

 

 

 

 

 

 

 

 

 

000

DMA has priority and does not negate its request

 

 

 

 

 

 

until transfer completes.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

001

512

 

16384

 

 

 

 

 

 

 

 

 

 

 

 

 

 

010

1024

 

32768

 

 

 

 

 

 

 

 

 

 

 

 

 

 

011

2048

 

65536

 

 

 

 

 

 

 

 

 

 

 

 

 

 

100

4096

 

131072

 

 

 

 

 

 

 

 

 

 

 

 

 

 

101

8192

 

262144

 

 

 

 

 

 

 

 

 

 

 

 

 

 

110

16384

 

524288

 

 

 

 

 

 

 

 

 

 

 

 

 

 

111

32768

 

1048576

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

24-23

Reserved, should be cleared.

 

 

 

 

 

 

 

 

 

 

 

22

SINC

Source increment. Controls whether a source address increments after each successful transfer.

 

 

0 No change to SAR after a successful transfer.

 

 

 

 

1 The SAR increments by 1, 2, 4, or 16, as determined by the transfer size.

 

 

 

 

 

 

 

21–20

SSIZE

Source size. Determines the data size of the source bus cycle for the DMA control module.

 

 

00

Longword

 

 

 

 

 

 

01

Byte

 

 

 

 

 

 

10

Word

 

 

 

 

 

 

11 Line (16-byte burst)

 

 

 

 

 

 

 

 

 

 

 

19

DINC

Destination increment. Controls whether a destination address increments after each successful transfer.

 

 

0 No change to the DAR after a successful transfer.

 

 

 

 

1 The DAR increments by 1, 2, 4, or 16, depending upon the size of the transfer.

 

 

 

 

 

 

 

18–17

DSIZE

Destination size. Determines the data size of the destination bus cycle for the DMA controller.

 

 

00

Longword

 

 

 

 

 

 

01

Byte

 

 

 

 

 

 

10

Word

 

 

 

 

 

 

11 Line (16-byte burst)

 

 

 

 

 

 

 

 

 

 

 

 

16

START

Start transfer.

 

 

 

 

 

 

0

DMA inactive

 

 

 

 

 

 

1 The DMA begins the transfer in accordance to the values in the control registers. START is cleared

 

 

 

automatically after one system clock and is always read as logic 0.

 

 

 

 

 

 

 

 

 

 

 

MOTOROLA

Chapter 16. DMA Controller Module

16-9

Page 349
Image 349
Motorola MCF5281, MCF5282 user manual Bwc, Encoding BCR24BIT =