ATMEGA640 datasheet(27/436 Pages) MICROCHIP

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ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

9. External Memory Interface

With all the features the External Memory Interface provides, it is well suited to operate as an interface to memory

devices such as External SRAM and Flash, and peripherals such as LCD-display, A/D, and D/A. The main features

are:

• Four different wait-state settings (including no wait-state)

• Independent wait-state setting for different External Memory sectors (configurable sector size)

• The number of bits dedicated to address high byte is selectable

• Bus keepers on data lines to minimize current consumption (optional)

9.1

Overview

When the eXternal MEMory (XMEM) is enabled, address space outside the internal SRAM becomes available

using the dedicated External Memory pins (see Figure 1-3 on page 4, Table 13-3 on page 75, Table 13-9 on page

79, and Table 13-21 on page 86). The memory configuration is shown in Figure 9-1.

Figure 9-1.

External Memory with Sector Select

9.1.1

Using the External Memory Interface

The interface consists of:

•

AD7:0: Multiplexed low-order address bus and data bus

A15:8: High-order address bus (configurable number of bits)

•

ALE: Address latch enable

•RD: Read strobe

•WR: Write strobe

Memory Configuration A

0x0000

0x21FF

External Memory

(0 - 60K x 8)

0xFFFF

Internal memory

SRL[2..0]

SRW11

SRW10

SRW01

SRW00

Lower sector

Upper sector

0x2200

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