Memories

1. Memories

2. 1. Flash Memory • Reprogrammable program Flash memory has the size of 8K x 16 bits (16KByte) by ATmega16. It has an endurance of at least 10,000 write/erase cycles. • Program Counter (PC) is 13 bit wide, thus it is capable of addressing the entire Program memory locations. • Program Flash memory space is divided in two sections, the Boot program section and the Application program section. ATmega16

3. Boot Memory Size is programmable thr’ fuses (128-1024 words(16bit)). • Boot Memory allows downloading and uploading program code by the μC itself. This feature allows flexible application software updates using a Flash-resident Boot Loader program.

4. 2. SRAM I/O Registers are control Registers for different functions like Communicat- ion functions, I/O Ports,…. ONLY I/O Registers $00 to $31 can be bit addressed: e.g. PORTA.3 means bit 3 of PORT A (see Register Summary in ATmega16 manual)

5. 3. EEPROM • 512 byte having an endurance of at least 100,000 write/erase cycles. • Write access time ≈ 8.5ms. • While read  CPU halted for 4 clock cycles • While write  CPU halted for 2 clock cycles

6. EEPROM I/O Registers • Address Register: • Data Register: • Control Register: Read Enable Write Enable Master Write Enable 1=set EEWE within 4cycles to write 0=no effect for settingEEWE Ready Interrupt-Enable generates an interrupt when EEWE is cleared

7. Program variables can be global (accessible to all the functions in the program) or local (accessible only inside the function they are declared). • If not specifically initialized, the global variables are automatically set to 0 at program startup. C Compiler: CodeVisionAVR

8. EEWE must be 0 Address Data EEMWE=1 Set EEWE within 4 clock cycles EEPROM WILL BE WRITEN IN Code while(EECR & 0x02) //wait until EEWE=0 #asm ("nop")//delay EEAR=2;//address=2 EEDR=5;//data=5 EECR.2=1; //Write logical one to EEMWE EECR.1=1; //Start eeprom write by setting //EEWE Write Sequence Preventing EEPROM corruption: Periods of low VCC can cause this corruption. Remedy: enabling the internal Brown-out Detector (BOD).

9. Specifying the EEPROM Storage Address for Global Variables • To store the integer variable "a“ in EEPROM at address 10h: eepromint a @0x10;

10. Status Register Bit 7 – I: Global Interrupt Enable Bit 6 – T: Bit Copy Storage Bit 5 – H: Half Carry Flag Bit 4 – S: Sign Bit, S = N ⊕ V Bit 3 – V: Two’s Complement Overflow Flag Bit 2 – N: Negative Flag Bit 1 – Z: Zero Flag Bit 0 – C: Carry Flag

11. Program Counter • The Program Counter keeps track of the location in flash program memory of the next instruction to be executed. • When the uC is reset, the Program Counter resets to 000000. • Every instruction fetched causes the Program Counter to increment by the number of bytes of this instruction. • Only by program jumps (conditional, unconditional and interrupts) the contents of the Program Counter are changed. • Also by interrupts, the Program Counter content is stored on the Stack(?) and a new program location is fetched, and on returning from interrupt the Program Counter regains its value.

12. Assignment: • The Atmega16 is used to control a lift in a 10 floor building. • Assume the average speed is 1m/s, and that the lift is moving on the average 6 hours every day, and that the distance between floors is 3m. • The EEPROM stores the number of each floor it passes by, so that when the supply is down and back again, the lift will recognize the floor it is at. • What other action can be done to let the controller recognize the floor? • What is the expected life of the controller? • Suggest a way for extending the life of the EEPROM. • Homing • The lift moves 6x3600 m/day=7200 floor/day=7200write/erase cycles • after 100,000/7200≈14 days the EEPROM will not accept data • Store location Cycling!