Datasheet

309
8011O–AVR–07/10
ATmega164P/324P/644P
24.8.2 Serial Programming Algorithm
When writing serial data to the ATmega164P/324P/644P, data is clocked on the rising edge of
SCK.
When reading data from the ATmega164P/324P/644P, data is clocked on the falling edge of
SCK. See Figure 24-12 for timing details.
To program and verify the ATmega164P/324P/644P in the serial programming mode, the follow-
ing sequence is recommended (See four byte instruction formats in Table 24-17):
1. 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”.
2. Wait for at least 20 ms and enable serial programming by sending the Programming
Enable serial instruction to pin MOSI.
3. The serial programming instructions will not work if the communication is out of synchro-
nization. When in sync. the second byte (0x53), 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 0x53 did not echo back, give RESET
a
positive pulse and issue a new Programming Enable command.
4. The Flash is programmed one page at a time. The memory page is loaded one byte at a
time by supplying the 7 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 address
lines 15..8. Before issuing this command, make sure the instruction Load Extended
Address Byte has been used to define the MSB of the address. The extended address
byte is stored until the command is re-issued, that is, the command needs only be issued
for the first page, and when crossing the 64KWord boundary. If polling (
RDY/BSY) is not
used, the user must wait at least t
WD_FLASH
before issuing the next page. (See Table 24-
16.) Accessing the serial programming interface before the Flash write operation com-
pletes can result in incorrect programming.
5. 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 24-16.) In a chip erased
device, no 0xFFs in the data file(s) need to be programmed.
6. Any memory location can be verified by using the Read instruction which returns the con-
tent at the selected address at serial output MISO. When reading the Flash memory, use
the instruction Load Extended Address Byte to define the upper address byte, which is
not included in the Read Program Memory instruction. The extended address byte is
stored until the command is re-issued, that is, the command needs only be issued for the
first page, and when crossing the 64KWord boundary.
7. At the end of the programming session, RESET
can be set high to commence normal
operation.
8. Power-off sequence (if needed):
Set RESET
to “1”.
Turn V
CC
power off.