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Break Microcontroller ATmega164 flash memory and extract ATmega164 MCU code from its secured memory, make ATmega164 processor cloning;

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) if recover mcu atmega2560 flash.

When the eXternal MEMory (XMEM) is enabled, address space outside the internal SRAM becomes available using the dedicated External Memory pins (see Figure 2 on page 3, Table 36 on page 88, Table 42 on page 92, and Table 54 on page 102). The memory configuration is shown in Figure 14.

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.

The control bits for the External Memory Interface are located in two registers, the External Memory Control Register A – XMCRA, and the External Memory Control Register B– XMCRB.

When the XMEM interface is enabled, the XMEM interface will override the setting in the data direction registers that corresponds to the ports dedicated to the XMEM interface.

For details about the port override, see the alternate functions in section “I/O-Ports” on page 81. The XMEM interface will auto-detect whether an access is internal or external if reverse engineering microcontroller atmega1281 program.

If the access is external, the XMEM interface will output address, data, and the control signals on the ports according to Figure 16 (this figure shows the wave forms without wait-states). When ALE goes from high-to-low, there is a valid address on AD7:0. ALE is low during a data transfer.

When the XMEM interface is enabled, also an internal access will cause activity on address, data and ALE ports, but the RD and WR strobes will not toggle during internal access. When the External Memory Interface is disabled, the normal pin and data direction settings are used.

Note that when the XMEM interface is disabled, the address space above the internal SRAM boundary is not mapped into the internal SRAM. Figure 15 illustrates how to connect an external SRAM to the AVR using an octal latch (typically “74 x 573” or equivalent) which is transparent when G is high.

Due to the high-speed operation of the XRAM interface, the address latch must be selected with care for system frequencies above 8 MHz @ 4V and 4 MHz @ 2.7V.

When operating at conditions above these frequencies, the typical old style 74HC series latch becomes inadequate. The External Memory Interface is designed in compliance to the 74AHC series latch. However, most latches can be used as long they comply with the main timing parameters. The main parameters for the address latch are:

D to Q propagation delay (tPD).

Data setup time before G low (tSU).

Data (address) hold time after G low (TH).

The External Memory Interface is designed to guaranty minimum address hold time after G is asserted low of th = 5 ns. Refer to tLAXX_LD/tLLAXX_ST in “External Data Memory Timing” Tables 169 through Tables 176 on pages 376 – 378.

The D-to-Q propagation delay (tPD) must be taken into consideration when calculating the access time requirement of the external component. The data setup time before G low (tSU) must not exceed address valid to ALE low (tAVLLC) minus PCB wiring delay (dependent on the capacitive load).

The pull-ups on the AD7:0 ports may be activated if the corresponding Port register is written to one. To reduce power consumption in sleep mode, it is recommended to disable the pull-ups by writing the Port register to zero before entering sleep.

The XMEM interface also provides a bus-keeper on the AD7:0 lines. The bus-keeper can be disabled and enabled in software as described in “External Memory Control Register B – XMCRB” on page 35. When enabled, the bus-keeper will keep the previous value on the AD7:0 bus while these lines are tri-stated by the XMEM interface.