AMD AMD-K6-2/400 User Guide - Page 277
TAP Registers, Test and Debug
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23542A/0-September 2000 Preliminary Information AMD-K6™-2E+ Embedded Processor Data Sheet TAP Registers Chapter 13 The AMD-K6-2E+ processor provides an Instruction Register (IR) and three Test Data Registers (TDR) to support the boundary-scan architecture. The IR and one of the TDRs-the Boundary-Scan Register (BSR)-consist of a shift register and an output register. The shift register is loaded in parallel in the Capture states. (See "TAP Controller State Machine" on page 260 for a description of the TAP controller states.) In addition, the shift register is loaded and shifted serially in the Shift states. The output register is loaded in parallel from its corresponding shift register in the Update states. Instruction Register (IR). The IR is a 5-bit register, without parity, that determines which instruction to run and which test data register to select. When the TAP controller enters the Capture-IR state, the processor loads the following bits into the IR shift register: s 01b-Loaded into the two least significant bits, as specified by the IEEE 1149.1 standard s 000b-Loaded into the three most significant bits Loading 00001b into the IR shift register during the Capture-IR state results in loading the SAMPLE/PRELOAD instruction. For each entry into the Shift-IR state, the IR shift register is serially shifted by one bit toward the TDO pin. During the shift, the most significant bit of the IR shift register is loaded from the TDI pin. The IR output register is loaded from the IR shift register in the Update-IR state, and the current instruction is defined by the IR output register. See "TAP Instructions" on page 259 for a list and definition of the instructions supported by the AMD-K6-2E+ processor. Boundary Scan Register (BSR). The Boundary Scan Register is a Test Data Register consisting of the interconnection of 152 boundary-scan cells. Each output and bidirectional pin of the processor requires a two-bit cell, where one bit corresponds to the pin and the other bit is the output enable for the pin. When a 0 is shifted into the enable bit of a cell, the corresponding pin is floated, and when a 1 is shifted into the enable bit, the pin is driven valid. Each input pin requires a one-bit cell that corresponds to the pin. The last cell of the BSR is reserved and does not correspond to any processor pin. Test and Debug 255