DSP56366 datasheet(9/110 Pages) FREESCALE

9 / 110 page

DSP56366 Technical Data, Rev. 3.1

Freescale Semiconductor

2-5

2.5.1

External Address Bus

2.5.2

External Data Bus

2.5.3

External Bus Control

Table 2-5 External Address Bus Signals

Signal

Name

Type

State

during

Reset

Signal Description

A0–A17

Output

Tri-stated

Address Bus—When the DSP is the bus master, A0–A17 are active-high outputs

that specify the address for external program and data memory accesses.

Otherwise, the signals are tri-stated. To minimize power dissipation, A0–A17 do not

change state when external memory spaces are not being accessed.

Table 2-6 External Data Bus Signals

Signal

Name

Type

State

during

Reset

Signal Description

D0–D23

Input/Output

Tri-stated

Data Bus—When the DSP is the bus master, D0–D23 are active-high,

bidirectional input/outputs that provide the bidirectional data bus for external

program and data memory accesses. Otherwise, D0–D23 are tri-stated.

Table 2-7 External Bus Control Signals

Signal Name

Type

State during

Reset

Signal Description

AA0–AA2/

RAS0–RAS2

Output

Tri-stated

Address Attribute or Row Address Strobe—When defined as AA, these

signals can be used as chip selects or additional address lines. When defined

as RAS, these signals can be used as RAS for DRAM interface. These signals

are tri-statable outputs with programmable polarity.

CAS

Output

Tri-stated

Column Address Strobe— When the DSP is the bus master, CAS is an

active-low output used by DRAM to strobe the column address. Otherwise, if the

bus mastership enable (BME) bit in the DRAM control register is cleared, the

signal is tri-stated.

Output

Tri-stated

Read Enable—When the DSP is the bus master, RD is an active-low output

that is asserted to read external memory on the data bus (D0-D23). Otherwise,

RD is tri-stated.

Output

Tri-stated

Write Enable—When the DSP is the bus master, WR is an active-low output

that is asserted to write external memory on the data bus (D0-D23). Otherwise,

WR is tri-stated.

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