ATMEGA640 datasheet(296/436 Pages) MICROCHIP

296 / 436 page

296

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

DS40002211A

28.3.1

Bypass Register

The Bypass Register consists of a single Shift Register stage. When the Bypass Register is selected as path

between TDI and TDO, the register is reset to 0 when leaving the Capture-DR controller state. The Bypass Regis-

ter can be used to shorten the scan chain on a system when the other devices are to be tested.

28.3.2

Device Identification Register

Figure 28-1 shows the structure of the Device Identification Register.

Figure 28-1. The Format of the Device Identification Register

28.3.2.1

Version

Version is a 4-bit number identifying the revision of the component. The JTAG version number follows the revision

of the device. Revision A is 0x0, revision B is 0x1 and so on.

28.3.2.2

Part Number

The part number is a 16-bit code identifying the component. The JTAG Part Number for ATme-

ga640/1280/1281/2560/2561 is listed in Table 30-6 on page 328.

28.3.2.3

Manufacturer ID

The Manufacturer ID is a 11-bit code identifying the manufacturer. The JTAG manufacturer ID for ATMEL is listed

in Table 30-6 on page 328.

28.3.3

Reset Register

The Reset Register is a test Data Register used to reset the part. Since the AVR tri-states Port Pins when reset,

the Reset Register can also replace the function of the un-implemented optional JTAG instruction HIGHZ.

A high value in the Reset Register corresponds to pulling the external Reset low. The part is reset as long as there

is a high value present in the Reset Register. Depending on the fuse settings for the clock options, the part will

remain reset for a reset time-out period (see “Clock Sources” on page 40) after releasing the Reset Register. The

output from this Data Register is not latched, so the reset will take place immediately, as shown in Figure 28-2 on

page 297.

MSB

LSB

Bit

Device ID

Version

Part Number

Manufacturer ID

4 bits

16 bits

11 bits

1-bit

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