9.5.2. Pullup resistors

The IEEE 1149.1 standard effectively requires TDI and TMS to have internal pullup resistors. In order to minimize static current draw, these resistors are not fitted to the ARM9TDMI core. Accordingly, the four inputs to the test interface (the TDO, TDI, and TMS signals, plus TCK) must all be driven to valid logic levels to achieve normal circuit operation.

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