Rainbow Electronics ATmega8515L - Manual (Page 190)

190
ATmega8515(L)
2512A–AVR–04/02
Serial Programming
Algorithm When writing serial data to the ATmega8515, data is clocked on the rising edge of SCK.
When reading data from the ATmega8515, data is clocked on the falling edge of SCK.
See Figure 84, Figure 85, and Table 95 for timing details.
To program and verify the ATmega8515 in the Serial Programming mode, the following
sequence is recommended (See four byte instruction formats in Table 94.):
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 serial programming by sending the Program-
ming Enable serial instruction to pin MOSI.
3. The Serial Programming instructions will not work if the communication is out of
synchronization. When in synchronization, 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 Program-
ming 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 5 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 93.
Accessing the serial programming interface before the Flash write operation
completes 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 93. In a chip erased device, no $FFs in the data file(s) need to be
programmed.
6. Any memory location can be verified by using the Read instruction which returns
the content at the selected address at serial output MISO.
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.
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 written. Note that the entire page is written simultaneously and any
address within the page can be used for polling. Data polling of the Flash will not work
for the value $FF, so when programming this value, the user will have to wait for at least
t
WD_FLASH
before programming the next page. As a chip erased device contains $FF in
all locations, programming of addresses that are meant to contain $FF, can be skipped.
See Table 93 for t
WD_FLASH
value.