Rainbow Electronics AT90LS4433 - Manual (Page 16)

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AT90S/LS4433
1042G–AVR–09/02
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
T1 T2 T3 T4
System Clock Ø
Total Execution Time
Register Operands Fetch
ALU Operation Execute
Result Write Back
T1 T2 T3 T4