Datasheet
378
ATmega16U4/32U4 [DATASHEET]
Atmel-7766J-USB-ATmega16U4/32U4-Datasheet_04/2016
8. The bit mapping for Fuses Low byte is listed in Table 28-5 on page 355.
9. The bit mapping for Lock bits byte is listed in Table 28-1 on page 353.
10. Address bits exceeding PCMSB and EEAMSB (Table 28-11 on page 359 and Table 28-12 on page 359) are don’t care.
11. All TDI and TDO sequences are represented by binary digits (0b...).
Figure 28-15. State Machine Sequence for Changing/Reading the Data Word
28.9.11 Flash Data Byte Register
The Flash Data Byte Register provides an efficient way to load the entire Flash page buffer before executing
Page Write, or to read out/verify the content of the Flash. A state machine sets up the control signals to the
Flash and senses the strobe signals from the Flash, thus only the data words need to be shifted in/out.
The Flash Data Byte Register actually consists of the 8-bit scan chain and a 8-bit temporary register. During
page load, the Update-DR state copies the content of the scan chain over to the temporary register and initiates
a write sequence that within 11 TCK cycles loads the content of the temporary register into the Flash page
buffer. The AVR automatically alternates between writing the low and the high byte for each new Update-DR
state, starting with the low byte for the first Update-DR encountered after entering the PROG_PAGELOAD
command. The Program Counter is pre-incremented before writing the low byte, except for the first written byte.
This ensures that the first data is written to the address set up by PROG_COMMANDS, and loading the last
location in the page buffer does not make the Program Counter increment into the next page.
During Page Read, the content of the selected Flash byte is captured into the Flash Data Byte Register during
the Capture-DR state. The AVR automatically alternates between reading the low and the high byte for each
Test-Logic-Reset
Run-Test/Idle
Shift-DR
Exit1-DR
Pause-DR
Exit2-DR
Update-DR
Select-IR Scan
Capture-IR
Shift-IR
Exit1-IR
Pause-IR
Exit2-IR
Update-IR
Select-DR Scan
Capture-DR
0
1
0
11 1
00
00
11
1
0
1
1
0
1
0
0
1
0
1
1
0
1
0
0
00
11