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AMD-K5 Processor
AMD K86 Family BIOS and Software Tools Developers Guide
21062E/0—June 1997
Preliminary Information
Instruction Register.
The 5-bit Instruction Register (IR) is a
serial-in parallel-out register that includes five shift
register-based cells for holding instruction data. The
instruction determines which test to run, which data register to
access, or both. When the TAP controller enters the Capture-IR
state, the processor loads the IDCODE instruction in the IR.
Executing Shift-IR starts instructions shifting into the
instruction register on the rising edge of TCK. Executing
Update-IR loads the instruction from the serial shift register to
the parallel register.
The TAP controller is a synchronous, finite-state machine that
controls the test and debug logic sequence of operations. The
TAP controller changes state in response to the rising edge of
TCK and defaults to the test logic reset state at power-up.
Reinitialization to the test logic reset state is accomplished by
holding the TMS pin High for five TCK periods.
JTAG Register
Organization
All registers in the JTAG logic consist of the following two
register ranks:
I
Shift register
Parallel output register fed by the shift register
I
Parallel input data is loaded into the shift register when the
TAP controller exits the Capture state (Capture-DR or
Capture-IR). The shift register then shifts data from TDI to
TDO when in the Shift state (Shift-DR or Shift-IR). The output
register holds the current data while new data is shifted into
the shift register. The contents of the output register are
updated when the TAP controller exits the Update state
(Update-DR or Update-IR). The following three registers are
described in this section:
I
Boundary Scan Register
Device Identification Register
Bypass Register
I
I
Boundary Scan Register.
The Boundary Scan Register (BSR) is a
261-bit shift register with cells connected to all input and
output pins and containing cells for tri-state I/O control. This
arrangement enables serial data to be loaded into or read from
the processor boundary scan area.