AT90LS4433-4AI datasheet(16/126 Pages) ATMEL

16 / 126 page

AT90S/LS4433

1042H–AVR–04/03

EEPROM Data Memory

The AT90S4433 contains 256 bytes of data EEPROM memory. It is organized as a sep-

arate data space, in which single bytes can be read and written. The EEPROM has an

endurance of at least 100,000 write/erase cycles per location. The access between the

EEPROM and the CPU is described on page 53, specifying the EEPROM Address Reg-

isters, the EEPROM Data Register and the EEPROM Control Register.

For the SPI Data downloading, see page 93 for a detailed description. The EEPROM

Data memory is In-System Programmable through the SPI port. Please refer to the

“EEPROM Read/Write Access” section on page 45 for a thorough description of

EEPROM access.

Memory Access Times

and Instruction

Execution Timing

This section describes the general access timing concepts for instruction execution and

internal memory access.

The AVR CPU is driven by the System Clock Ø, directly generated from the external

clock crystal for the chip. No internal clock division is used.

Figure 21 shows the parallel instruction fetches and instruction executions enabled by

the Harvard architecture and the fast-access Register File concept. This is the basic

pipelining concept to obtain up to 1 MIPS per MHz with the corresponding unique results

for functions per cost, functions per clocks and functions per power unit.

Figure 21. The Parallel Instruction Fetches and Instruction Executions

Figure 22 shows the internal timing concept for the Register File. In a single clock cycle

an ALU operation using two register operands is executed and the result is stored back

to the destination register.

Figure 22. Single Cycle ALU Operation

The internal data SRAM access is performed in two System Clock cycles as described

in Figure 23.

System Clock Ø

1st Instruction Fetch

1st Instruction Execute

2nd Instruction Fetch

2nd Instruction Execute

3rd Instruction Fetch

3rd Instruction Execute

4th Instruction Fetch

System Clock Ø

Total Execution Time

ALU Operation Execute

Result Write Back

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