Datasheet
699
32133D–11/2011
UC3D
• Perform a CHIP_ERASE to clear the security bit. NOTE: This will erase all the contents of the
non-volatile memory.
31.6 JTAG Instruction Summary
The implemented JTAG instructions in the 32-bit AVR are shown in the table below.
31.6.1 Security Restrictions
When the security fuse in the Flash is programmed, the following JTAG instructions are
restricted:
• NEXUS_ACCESS
• MEMORY_WORD_ACCESS
• MEMORY_BLOCK_ACCESS
• MEMORY_SIZED_ACCESS
For description of what memory locations remain accessible, please refer to the SAB address
map.
Full access to these instructions is re-enabled when the security fuse is erased by the
CHIP_ERASE JTAG instruction.
Table 31-38. JTAG Instruction Summary
Instruction
OPCODE Instruction Description
0x01 IDCODE Select the 32-bit Device Identification register as data register.
0x02 SAMPLE_PRELOAD Take a snapshot of external pin values without affecting system operation.
0x03 EXTEST
Select boundary-scan chain as data register for testing circuitry external to
the device.
0x04 INTEST Select boundary-scan chain for internal testing of the device.
0x06 CLAMP
Bypass device through Bypass register, while driving outputs from boundary-
scan register.
0x0C AVR_RESET Apply or remove a static reset to the device
0x0F CHIP_ERASE Erase the device
0x10 NEXUS_ACCESS
Select the SAB Address and Data registers as data register for the TAP. The
registers are accessed in Nexus mode.
0x11 MEMORY_WORD_ACCESS Select the SAB Address and Data registers as data register for the TAP.
0x12 MEMORY_BLOCK_ACCESS
Select the SAB Data register as data register for the TAP. The address is
auto-incremented.
0x13 CANCEL_ACCESS Cancel an ongoing Nexus or Memory access.
0x14 MEMORY_SERVICE
Select the SAB Address and Data registers as data register for the TAP. The
registers are accessed in Memory Service mode.
0x15 MEMORY_SIZED_ACCESS Select the SAB Address and Data registers as data register for the TAP.
0x17 SYNC Synchronization counter
0x1C HALT Halt the CPU for safe programming.
0x1F BYPASS Bypass this device through the bypass register.
Others N/A Acts as BYPASS