ATmega165 datasheet(266/336 Pages) ATMEL

266 / 336 page

266

ATmega165/V

2573G–AVR–07/09

SPI Serial Programming

Characteristics

For characteristics of the SPI module see “SPI Timing Characteristics” on page 282.

Programming via the

JTAG Interface

Programming through the JTAG interface requires control of the four JTAG specific

pins: TCK, TMS, TDI, and TDO. Control of the reset and clock pins is not required.

To be able to use the JTAG interface, the JTAGEN Fuse must be programmed. The

device is default shipped with the fuse programmed. In addition, the JTD bit in MCUCSR

must be cleared. Alternatively, if the JTD bit is set, the external reset can be forced low.

Then, the JTD bit will be cleared after two chip clocks, and the JTAG pins are available

for programming. This provides a means of using the JTAG pins as normal port pins in

Running mode while still allowing In-System Programming via the JTAG interface. Note

that this technique can not be used when using the JTAG pins for Boundary-scan or On-

chip Debug. In these cases the JTAG pins must be dedicated for this purpose.

During programming the clock frequency of the TCK Input must be less than the maxi-

mum frequency of the chip. The System Clock Prescaler can not be used to divide the

TCK Clock Input into a sufficiently low frequency.

As a definition in this datasheet, the LSB is shifted in and out first of all Shift Registers.

Programming Specific JTAG

Instructions

The Instruction Register is 4-bit wide, supporting up to 16 instructions. The JTAG

instructions useful for programming are listed below.

The OPCODE for each instruction is shown behind the instruction name in hex format.

The text describes which Data Register is selected as path between TDI and TDO for

each instruction.

The Run-Test/Idle state of the TAP controller is used to generate internal clocks. It can

also be used as an idle state between JTAG sequences. The state machine sequence

for changing the instruction word is shown in Figure 122.

ATmega165 bảng dữ liệu(PDF) 266 Page - ATMEL Corporation