The IEEE Std. 1149.1 specifies both mandatory and optional device features. Mandatory features include the following:
- Every IEEE-1149.1 compliant device has to have implemented the following registers:
- Bypass Register (1 bit long, capture value binary ‘0’)
- Boundary Scan Register (design dependent length)
- Instruction Register (at least two bit long, capture value binary ‘xx…01’)
- Every IEEE-1149.1 compliant device has to support the following test instructions:
- BYPASS (opcode binary ’11…1’, and perhaps others)
- SAMPLE (opcode defined by component designer)
- PRELOAD (may be combined with SAMPLE, opcode defined by component designer)
- EXTEST (opcode defined by component designer)
- Every IEEE-1149.1 compliant device has to provide four test bus signals:
- TCK (Test Clock)
- TMS (Test Mode Select)
- TDI (Test Data In)
- TDO (Test Data Out)
- Any negation of signal values within the Boundary Scan register is not permitted.
- Internal pull-up resistors are required on TDI and TMS.
- Avoid Ground-Bounce problems.
For a complete description of all mandatory features refer to the IEEE Std. 1149.1-2001 specification.
