ATMEGA640 datasheet(350/436 Pages) MICROCHIP

350 / 436 page

350

ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

Figure 30-16. State Machine Sequence for Changing/Reading the Data Word

30.9.11

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 Pro-

gram 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 Cap-

ture-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

ATMEGA640 Datasheet(PDF) 350 Page - Microchip Technology