2.1. JTAG Circuitry Functional Model
The JTAG BST circuitry requires the following registers:
- Instruction register—determines which action to perform and which data register to access.
- Bypass register (1-bit long data register)—provides a minimum-length serial path between the TDI and TDO pins.
- Boundary-scan register—shift register composed of all the BSCs of the device.
- Test access port (TAP) controller—controls the JTAG BST.
- TMS and TCK pins—operate the TAP controller.
- TDI and TDO pins—provide the serial path for the data and instruction registers.
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