Datasheet

Signal Name in
Programming Mode
Pin Name I/O Function
WR PD3 I Write Pulse (Active low)
BS1 PD4 I Byte Select 1 (“0” selects Low byte, “1” selects High byte)
XA0 PD5 I XTAL Action Bit 0
XA1 PD6 I XTAL Action Bit 1
PAGEL PD7 I Program memory and EEPROM Data Page Load
BS2 PC2 I Byte Select 2 (“0” selects Low byte, “1” selects 2’nd High
byte)
DATA PB[7:0] I/O Bi-directional Data bus (Output when OE is low)
Table 28-13. BS2 and BS1 encoding.
BS2 BS1 Flash / EEPROM
address
Flash data
loading / reading
Fuse programming Reading fuse and lock
bits
0 0 Low Byte Low Byte Low Byte Fuse Low Byte
0 1 High Byte High Byte High Byte Lockbits
1 0 Extended High Byte Reserved Extended Byte Extended Fuse Byte
1 1 Reserved Reserved Reserved Fuse High Byte
Table 28-14. Pin Values Used to Enter Programming Mode
Pin Symbol Value
PAGEL Prog_enable[3] 0
XA1 Prog_enable[2] 0
XA0 Prog_enable[1] 0
BS1 Prog_enable[0] 0
Table 28-15. XA1 and XA0 Coding
XA1 XA0 Action when XTAL1 is Pulsed
0 0 Load Flash or EEPROM Address (High or low address byte determined by 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 28-16. Command Byte Bit Coding
Command Byte Command Executed
1000 0000 Chip Erase
0100 0000 Write Fuse bits
Atmel ATmega644A [DATASHEET]
Atmel-42716C-ATmega644A_Datasheet_Complete-10/2016
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