AT83C5136-RDTUL datasheet(27/171 Pages) ATMEL

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AT83C5134/35/36

7683B–USB–03/07

Table 32. External Data Memory Interface Signals

External Bus Cycles

This section describes the bus cycles the AT83C5134/35/36 executes to fetch code

(see Figure 15) in the external program/code memory.

External memory cycle takes 6 CPU clock periods. This is equivalent to 12 oscillator

clock periods in standard mode or 6 oscillator clock periods in X2 mode. For further

information on X2 mode (see the clock Section).

For simplicity, the accompanying figure depicts the bus cycle waveforms in idealized

form and do not provide precise timing information.

Figure 15. External Code Fetch Waveforms

Signal

Name

Type

Description

Alternate

Function

A15:8

Address Lines

Upper address lines for the external bus.

P2.7:0

AD7:0

I/O

Address/Data Lines

Multiplexed lower address lines and data for the external memory.

P0.7:0

ALE

Address Latch Enable

ALE signals indicates that valid address information are available on lines

AD7:0.

PSEN

Program Store Enable Output

This signal is active low during external code fetch or external code read

(MOVC instruction).

ALE

PSEN

PCL

PCH

PCL

D7:0

PCH

D7:0

CPU Clock

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