ATmega16 datasheet(274/357 Pages) ATMEL

274 / 357 page

274

2466S–AVR–05/09

ATmega16(L)

tion. The Chip Erase operation turns the content of every memory location in both the Program

and EEPROM arrays into $FF.

Depending on CKSEL Fuses, a valid clock must be present. The minimum low and high periods

for the serial clock (SCK) input are defined as follows:

Low:> 2 CPU clock cycles for f

ck < 12 MHz, 3 CPU clock cycles for fck

12 MHz

High:> 2 CPU clock cycles for f

ck < 12 MHz, 3 CPU clock cycles for fck

12 MHz

SPI Serial

Programming

Algorithm

When writing serial data to the ATmega16, data is clocked on the rising edge of SCK.

When reading data from the ATmega16, data is clocked on the falling edge of SCK. See Figure

138 for timing details.

To program and verify the ATmega16 in the SPI Serial Programming mode, the following

sequence is recommended (See four byte instruction formats in Figure 116 on page 276

Power-up sequence:

Apply power between V

CC and GND while RESET and SCK are set to “0”. In some sys-

tems, the programmer can not guarantee that SCK is held low during power-up. In this

case, RESET must be given a positive pulse of at least two CPU clock cycles duration

after SCK has been set to “0”.

Wait for at least 20 ms and enable SPI Serial Programming by sending the Programming

Enable serial instruction to pin MOSI.

The SPI Serial Programming instructions will not work if the communication is out of syn-

chronization. When in sync. the second byte ($53), will echo back when issuing the third

byte of the Programming Enable instruction. Whether the echo is correct or not, all four

bytes of the instruction must be transmitted. If the $53 did not echo back, give RESET a

positive pulse and issue a new Programming Enable command.

The Flash is programmed one page at a time. The page size is found in Table 107 on page

262

. The memory page is loaded one byte at a time by supplying the 6 LSB of the

address and data together with the Load Program Memory Page instruction. To ensure

correct loading of the page, the data Low byte must be loaded before data High byte is

applied for a given address. The Program Memory Page is stored by loading the Write

Program Memory Page instruction with the 7 MSB of the address. If polling is not used,

the user must wait at least t

WD_FLASH before issuing the next page. (See Table 115).

Accessing the SPI Serial Programming interface before the Flash write operation com-

pletes can result in incorrect programming.

The EEPROM array is programmed one byte at a time by supplying the address and data

together with the appropriate Write instruction. An EEPROM memory location is first

automatically erased before new data is written. If polling is not used, the user must wait

at least t

WD_EEPROM before issuing the next byte. (See Table 115). In a chip erased device,

no $FFs in the data file(s) need to be programmed.

Any memory location can be verified by using the Read instruction which returns the con-

tent at the selected address at serial output MISO.

At the end of the programming session, RESET can be set high to commence normal

operation.

Power-off sequence (if needed):

Set RESET to “1”.

Turn V

CC power off.

Data Polling Flash

When a page is being programmed into the Flash, reading an address location within the page

being programmed will give the value $FF. At the time the device is ready for a new page, the

programmed value will read correctly. This is used to determine when the next page can be writ-

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