AMD AMD-K6-2/500AFX Data Sheet - Page 243
BoundaryScan Test Access Port (TAP), Test Access Port, TAP Signals
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21850J/0-February 2000 Preliminary Information AMD-K6®-2 Processor Data Sheet 11.3 Boundary-Scan Test Access Port (TAP) Test Access Port TAP Signals The boundary-scan Test Access Port (TAP) is an IEEE standard that defines synchronous scanning test methods for complex logic circuits, such as boards containing a processor. The AMD-K6-2 processor supports the TAP standard defined in the IEEE Standard Test Access Port and Boundary-Scan Architecture (IEEE 1149.1-1990) specification. Boundary scan testing uses a shift register consisting of the serial interconnection of boundary-scan cells that correspond to each I/O buffer of the processor. This non-inverting register chain, called a Boundary Scan Register (BSR), can be used to capture the state of every processor pin and to drive every processor output and bidirectional pin to a known state. Each BSR of every component on a board that implements the boundary-scan architecture can be serially interconnected to enable component interconnect testing. The TAP consists of the following: s Test Access Port (TAP) Controller-The TAP controller is a synchronous, finite state machine that uses the TMS and TDI input signals to control a sequence of test operations. See "TAP Controller State Machine" on page 232 for a list of TAP states and their definition. s Instruction Register (IR)-The IR contains the instructions that select the test operation to be performed and the Test Data Register (TDR) to be selected. See "TAP Registers" on page 224 for more details on the IR. s Test Data Registers (TDR)-The three TDRs are used to process the test data. Each TDR is selected by an instruction in the Instruction Register (IR). See "TAP Registers" on page 224 for a list of these registers and their functions. The test signals associated with the TAP controller are as follows: s TCK-The Test Clock for all TAP operations. The rising edge of TCK is used for sampling TAP signals, and the falling edge of TCK is used for asserting TAP signals. The state of the TMS signal sampled on the rising edge of TCK causes Chapter 11 Test and Debug 223