Rainbow-electronics ATmega8515L Manuel d'utilisateur télécharger pdf (Page 23)

ATmega8515(L)

2512A–AVR–04/02

Figure 11. ExternalMemory withSectorSelect

Using the External Memory

Interface

Theinterface consists of:

•AD7:0:Multiplexedlow-order address bus anddata bus

•A15:8:High-order address bus(configurable number ofbits)

•ALE: Address latch enable

•RD

: Readstrobe

• WR

:Write strobe

The controlbitsfor the ExternalMemory Interfaceare located in three registers, the

MCU Control Register – MCUCR, the ExtendedMCUControl Register – EMCUCR, and

the SpecialFunction IO Register – SFIOR.

When the XMEM interfaceis enabled, it will overridethe settings in the data direction

registers correspondingtothe portsdedicated to theinterface. Fordetails about thisport

override,see thealternate functions in section “I/O Ports”onpage 56.The XMEM inter-

face will auto-detect whether an access is internal or external. If theaccess is external,

the XMEM interface will output address, data, and the controlsignals on the ports

according to Figure13(thisfigure shows the wave formswithout wait states). When

ALE goesfrom high to low, thereis avalid address on AD7:0. ALE islowduring a data

transfer. When the XMEM interfaceis enabled, alsoaninternal access will causeactiv-

ity on address-, data-, and ALE ports, but theRD

andWR strobeswill not toggle during

internal access. When the ExternalMemory Interfaceisdisabled, thenormalpin and

0x0000

0x25F

External Memory

(0-64K x 8)

0xFFFF

Internal Memory

SRL[2..0]

SRW11

SRW10

SRW01

SRW00

Lower Sector

Upper Sector

0x260

1 2 ... 18 19 20 21 22 23 24 25 26 27 28 ... 222 223

Pas de commentaire

Rainbow-electronics ATmega8515L Manuel d'utilisateur Page 23