ATmega165 datasheet(213/336 Pages) ATMEL

213 / 336 page

213

ATmega165/V

2573G–AVR–07/09

Bypass Register

The Bypass Register consists of a single Shift Register stage. When the Bypass Regis-

ter is selected as path between TDI and TDO, the register is reset to 0 when leaving the

Capture-DR controller state. The Bypass Register can be used to shorten the scan

chain on a system when the other devices are to be tested.

Device Identification Register

Figure 99 shows the structure of the Device Identification Register.

Figure 99. The Format of the Device Identification Register

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.

Part Number

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

ATmega165 is listed in Table 104 on page 249. Note that the JTAG Part Number is the

same as ATmega169.

Manufacturer ID

The Manufacturer ID is a 11-bit code identifying the manufacturer. The JTAG manufac-

turer ID for ATMEL is listed in Table 105 on page 249.

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

unimplemented 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 (refer to “Clock Sources” on page 24) after releasing the Reset Register. The out-

put from this Data Register is not latched, so the reset will take place immediately, as

shown in Figure 100.

Figure 100. Reset Register

MSB

LSB

Bit

Device ID

Version

Part Number

Manufacturer ID

4 bits

16 bits

11 bits

1-bit

From

TDI

ClockDR · AVR_RESET

TDO

From Other Internal and

External Reset Sources

Internal reset

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