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Special Pins

Special Pins. A Very Basic Topic But A Source of Frequent Failures and Problems. Termination of Special Pins. MODE pin (test program mode). V PP pin (programming voltage). TRST* (Reset to JTAG TAP controller) TCLK (provides clock to TAP controller) SDI, DCLK (varies for each device type)

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Special Pins

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  1. Special Pins A Very Basic Topic But A Source of Frequent Failures and Problems

  2. Termination of Special Pins • MODE pin (test program mode). • VPP pin (programming voltage). • TRST* (Reset to JTAG TAP controller) • TCLK (provides clock to TAP controller) • SDI, DCLK (varies for each device type) • Others

  3. MODE Pin • Left Floating • Device can be non-functional • High currents • Uncontrolled I/O • Tied High During Test • Working device stopped functioning • Power supply rise time key

  4. MODE Register Y1 Register Y2 Register X2 Register X1 Register Other Registers MODE Pin - Test, Debug and Programming Control

  5. MODE Pin - Test, Debug and Programming Control

  6. CLK TCLK OSC IEEE JTAG 1149.1 TCLK The CLK pin may turn into an output driving low, clamping the oscillator’s output at a logic ‘0’. The TAP controller can not reset and restore I/O operation. Most FPGAs do not have the optional TRST* pin. Note TRST*, when present, has a pull-up.

  7. IEEE JTAG 1149.1 TCLK Shift Register is undefined in TEST-LOGIC-RESET State TAP Controller (State Machine) TCK Shift CLK TDI Shift Register TDO Reset Chip Control Parallel Latch Latch

  8. SYSTEM BIDIRECTIONAL OUTPUT IEEE JTAG 1149.1 - Scan Path SERIAL INPUT SERIAL INPUT SYSTEM SCAN 2 - STATE CELL OUTPUT SCAN SYSTEM CELL LOGIC SCAN SYSTEM EN CELL INPUT 3 - STATE SCAN OUTPUT CELL ON-CHIP LOGIC SCAN CELL EN SCAN SCAN CELL CELL

  9. IEEE JTAG 1149.1 - Scan I/O Cell To Next Pin Out Enable System Logic Data Out Data In JTAG DATA PATH

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