Rainbow Electronics ATmega162V - Manual (Page 245)

245
ATmega162/V
2513E–AVR–09/03
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 f
ck
>= 12 MHz
High:> 2 CPU clock cycles for f
ck
< 12 MHz, 3 CPU clock cycles for f
ck
>= 12 MHz
SPI Serial Programming
Algorithm When writing serial data to the ATmega162, data is clocked on the rising edge of SCK.
When reading data from the ATmega162, data is clocked on the falling edge of SCK.
See Figure 106.
To program and verify the ATmega162 in the SPI Serial Programming mode, the follow-
ing sequence is recommended (See four byte instruction formats in Table 111
):
1. Power-up sequence:
Apply power between V
CC
and GND while RESET and SCK are set to “0”. In
some systems, 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 SPI Serial Programming by sending the Pro-
gramming Enable serial instruction to pin MOSI.
3. The SPI Serial Programming instructions will not work if the communication is
out of synchronization. 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 Program-
ming Enable command.
4. The Flash is programmed one page at a time. The page size is found in Table
106 on page 235. 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 8 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 110.) Accessing the SPI
serial programming interface before the Flash write operation completes can
result in incorrect programming.
5. The EEPROM array can either be programmed one page at a time or it can be
programmed byte by byte.
For Page Programming, the following algorithm is used:
The EEPROM memory page is loaded one byte at a time by supplying the 2 LSB of
the address and data together with the Load EEPROM Memory Page instruction.
The EEPROM Memory Page is stored by loading the Write EEPROM Memory Page
instruction with the 8 MSB of the address. If polling is not used, the user must wait at
least t
WD_EEPROM
before issuing the next page. (See Table 100.) Accessing the SPI
Serial Programming interface before the EEPROM write operation completes can
result in incorrect programming.
Alternatively, the EEPROM can be programmed bytewise:
The EEPROM array is programmed one byte at a time by supplying the address
and data together with the Write EEPROM instruction. An EEPROM memory loca-
tion 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 110.) In
a chip erased device, no 0xFFs in the data file(s) need to be programmed.