ATmega16 datasheet(18/357 Pages) ATMEL

18 / 357 page

2466S–AVR–05/09

ATmega16(L)

Data Memory Access

Times

This section describes the general access timing concepts for internal memory access. The

internal data SRAM access is performed in two clk

CPU cycles as described in Figure 10.

Figure 10. On-chip Data SRAM Access Cycles

EEPROM Data

Memory

The ATmega16 contains 512 bytes of data EEPROM memory. It is organized as a separate data

space, in which single bytes can be read and written. The EEPROM has an endurance of at

least 100,000 write/erase cycles. The access between the EEPROM and the CPU is described

in the following, specifying the EEPROM Address Registers, the EEPROM Data Register, and

the EEPROM Control Register.

For a detailed description of SPI, JTAG, and Parallel data downloading to the EEPROM, see

page 273, page 278, and page 262, respectively.

EEPROM Read/Write

Access

The EEPROM Access Registers are accessible in the I/O space.

The write access time for the EEPROM is given in Table 1. A self-timing function, however, lets

the user software detect when the next byte can be written. If the user code contains instructions

that write the EEPROM, some precautions must be taken. In heavily filtered power supplies, V

is likely to rise or fall slowly on Power-up/down. This causes the device for some period of time

to run at a voltage lower than specified as minimum for the clock frequency used. See “Prevent-

ing EEPROM Corruption” on page 22 for details on how to avoid problems in these situations.

In order to prevent unintentional EEPROM writes, a specific write procedure must be followed.

Refer to the description of the EEPROM Control Register for details on this.

When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is

executed. When the EEPROM is written, the CPU is halted for two clock cycles before the next

instruction is executed.

clk

Data

Address

Address Valid

Compute Address

CPU

Memory Access Instruction

Next Instruction

ATmega16 데이터시트(PDF) 18 Page - ATMEL Corporation