ATMEGA8U2_14 Datasheet, PDF (251/310 Pages) ATMEL Corporation – 125 Powerful Instructions – Most Single Clock Cycle Execution

7799D–AVR–11/10
ATmega8U2/16U2/32U2
Table 25-9. Pin Name Mapping
Signal Name in
Programming Mode
Pin Name
PAGEL
PD7
BS2
PC6
DATA
PB7-0
I/O Function
I Program Memory and EEPROM data Page Load.
I Byte Select 2.
I/O Bi-directional Data bus (Output when OE is low).
Table 25-10. BS2 and BS1 Encoding
Flash Data
Flash / EEPROM Loading /
BS2 BS1 Address
Reading
0
0
Low Byte
Low Byte
0
1
High Byte
High Byte
1
0
Extended High
Byte
Reserved
1
1
Reserved
Reserved
Fuse
Programming
Low Byte
High Byte
Extended Byte
Reserved
Table 25-11. Pin Values Used to Enter Programming Mode
Pin
Symbol
PAGEL
Prog_enable[3]
XA1
Prog_enable[2]
XA0
Prog_enable[1]
BS1
Prog_enable[0]
Reading Fuse
and Lock Bits
Fuse Low Byte
Lockbits
Extended Fuse
Byte
Fuse High Byte
Value
0
0
0
0
Table 25-12. XA1 and XA0 Encoding
XA1
XA0
Action when XTAL1 is Pulsed
0
0
Load Flash or EEPROM Address (High or low address byte determined
by BS2 and BS1).
0
1
Load Data (High or Low data byte for Flash determined by BS1).
1
0
Load Command
1
1
No Action, Idle
Table 25-13. Command Byte Bit Encoding
Command Byte
Command Executed
1000 0000
Chip Erase
0100 0000
Write Fuse bits
0010 0000
Write Lock bits
0001 0000
Write Flash
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