ARM Technical Support Knowledge Articles

Do the test vectors check the TAP controller ID code?

Applies to: ARM7TDMI

Answer

The TAP controller IDCODE is checked only by the parallel scan vectors.

The IDCODE is provided by 32 transistors with their sources tied to either Vdd or Gnd, and can be changed by altering one metal layer in the layout.

If the IDCODE is changed by the ASIC designer, the netlist for layout verification as well as the test vectors must be modified to run without errors.

Note that there is no parallel output from the ID register for the ARM7 family. The least significant bit of the register is scanned out first.

For the rev3 ARM7TDMI, the default IDCODE is 0x3F0F0F0F

See also:

Article last edited on: 2008-09-09 15:47:36

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