AT90USB646 datasheet(387/434 Pages) ATMEL

387 / 434 page

387

7593A–AVR–02/06

AT90USB64/128

Note:

a = address high bits, b = address low bits, c = address extended bits, H = 0 - Low byte, 1 - High Byte, o = data out, i = data in,

x = don’t care

29.8.2

Serial Programming Characteristics

For characteristics of the Serial Programming module see “SPI Timing Characteristics” on page

405.

29.9 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-Sys-

tem 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 ded-

icated for this purpose.

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

quency 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.

29.9.1

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 29-12.

Read Extended Fuse Bits

0101 0000

0000 1000

xxxx xxxx

oooo oooo

Read Extended Fuse bits. “0” = pro-

grammed, “1” = unprogrammed. See

Table 29-3 on page 369 for details.

Read Calibration Byte

0011 1000

000x xxxx

0000 0000

oooo oooo

Read Calibration Byte

Poll RDY/BSY

1111 0000

0000 0000

xxxx xxxx

xxxx xxxo

o = “1”, a programming operation is

still busy. Wait until this bit returns to

“0” before applying another command.

Table 29-16. Serial Programming Instruction Set (Continued)

Instruction

Instruction Format

Operation

Byte 1

Byte 2

Byte 3

Byte4

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