Read MCU ATmega461A Software from embedded memory, clone microcontroller atmega461a program and data to new ones for the same functions, the protection of mcu atmega461a will be broken and decap for internal access the databus.
The ATMEGA461A is a complex microcontroller with more peripheral units than can be supported within the 64 location reserved in the Opcode for the IN and OUT instructions.
For the Extended I/O space from $060 – $1FF in SRAM, only the ST/STS/STD and LD/LDS/LDD instructions can be used. The first 4,608/8,704 Data Memory locations address both the Register File, the I/O Memory, Extended I/O Memory, and the internal data SRAM.
The first 32 locations address the Register file, the next 64 location the standard I/O Memory, then 416 locations of Extended I/O memory and the next 8,192 locations address the internal data SRAM.
An optional external data SRAM can be used with the ATmega640/1280/1281/2560/2561. This SRAM will occupy an area in the remaining address locations in the 64K address space. This area starts at the address following the internal SRAM.
The Register file, I/O, Extended I/O and Internal SRAM occupies the lowest 4,608/8,704 bytes, so when using 64KB (65,536 bytes) of External Memory, 60,478/56,832 Bytes of External Memory are available. See “External Memory Interface” on page 29 for details on how to take advantage of the external memory map.
When the addresses accessing the SRAM memory space exceeds the internal data memory locations, the external data SRAM is accessed using the same instructions as for the internal data memory access. When the internal data memories are accessed, the read and write strobe pins (PG0 and PG1) are inactive during the whole access cycle.
External SRAM operation is enabled by setting the SRE bit in the XMCRA Register. Accessing external SRAM takes one additional clock cycle per byte compared to access of the internal SRAM.
This means that the commands LD, ST, LDS, STS, LDD, STD, PUSH, and POP take one additional clock cycle. If the Stack is placed in external SRAM, interrupts, subroutine calls and returns take three clock cycles extra because the three-byte program counter is pushed and popped, and external memory access does not take advantage of the internal pipe-line memory access after Read MCU.
When external SRAM interface is used with wait-state, one-byte external access takes two, three, or four additional clock cycles for one, two, and three wait-states respectively. Interrupts, subroutine calls and returns will need five, seven, or nine clock cycles more than specified in the instruction set manual for one, two, and three wait-states.
The five different addressing modes for the data memory cover: Direct, Indirect with Displacement, Indirect, Indirect with Pre-decrement, and Indirect with Post-increment. In the Register file, registers R26 to R31 feature the indirect addressing pointer registers.
The direct addressing reaches the entire data space. The Indirect with Displacement mode reaches 63 address locations from the base address given by the Y- or Z-register.
When using register indirect addressing modes with automatic pre-decrement and post increment, the address registers X, Y, and Z are decremented or incremented.
The 32 general purpose working registers, 64 I/O registers, and the 4,196/8,192 bytes of internal data SRAM in the ATmega640/1280/1281/2560/2561 are all accessible through all these addressing modes. The Register File is described in “General Purpose Register File” on page 12.
