DSP56600FMSLASHAD datasheet(21/76 Pages) NXP

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Pin and Signal Descriptions

DSP56651 Signal Description

Preliminary

MOTOROLA

DSP56651 Technical Data Sheet

1-15

Data Bus

Bus Control

Table 1-8

Data Bus Signals

Signal

Names

Signal

Type

State

during

Reset

Signal Description

D0–D15

Input/

Output

Input

Data bus

—These signals provide the bidirectional data bus for

external memory accesses. D0–D15 are held in the previous logic

state when there is no external bus activity and during hardware

reset. This is done with weak “keepers” inside the I/O buffers.

Table 1-9

Bus Control Signals

Signal

Name

Signal

Type

State

during

Reset

Signal Description

R/W

Output

Driven

high

Read/write—

This signal indicates the bus access type. A high signal

indicates a bus read. A low signal indicates a write to the bus. When

accessing memory it can also be used as write enable (WE) signal. When

accessing a peripheral chip, the signal acts as a read/write.

EB0

Output

Driven

high

Enable byte 0

—When driven low, this signal indicates access to data

byte 0 (D8–D15) during a read or write cycle. This pin may also act as a

write byte enable, if so programmed. This output is used when accessing

16-bit wide SRAM.

EB1

Output

Driven

high

Enable byte 1

—When driven low, this signal indicates access to data

byte 1 (D0–D7) during a read or write cycle. This pin may also act as a

write byte enable, if so programmed. This output is used when accessing

16-bit wide SRAM.

Output

Driven

high

Bus select—

When driven low, this signal indicates that the current bus

access is a read cycle and enables slave devices to drive the data bus with

a read.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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