Datasheet

ATmega164A/PA/324A/PA/644A/PA/1284/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 321
Figure 27-16. State machine sequence for changing/reading the data word
27.10.11Flash 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
new Capture-DR state, starting with the low byte for the first Capture-DR encountered after entering the
PROG_PAGEREAD command. The Program Counter is post-incremented after reading each high byte,
including the first read byte. This ensures that the first data is captured from the first address set up by
PROG_COMMANDS, and reading the last location in the page makes the program counter increment into the
next page.
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