
Debug Using the Serial Interface and TAP Controller
Copyright 2000-2001 by LSI Logic Corporation. All rights reserved.
9-11
IDCODE (1110)
The IDCODE instruction connects the Device Identification (ID) register
between TDI and TDO. The ID register is a 32-bit register that allows the
manufacturer, part number, and version of a component to be determined
through the TAP. The ID register is loaded from the TAPID[31:0] input bus.
This input must be tied to a constant value that provides a unique device ID
code.
When the instruction register is loaded with the IDCODE instruction, all the
scan cells are placed in their normal (system) mode of operation.
In the CAPTURE-DR state, the ID register captures the device identification
code.
In the SHIFT-DR state, the previously captured device identification code is
shifted out of the ID register on TDO, while data is shifted into the ID register
through the TDI pin.
In the UPDATE-DR state, the ID register is not changed.
BYPASS (1111)
The BYPASS instruction connects the 1-bit shift Bypass register between TDI
and TDO.
When the BYPASS instruction is loaded into the instruction register, all the
scan cells are placed in their normal (system) mode of operation. This
instruction has no effect on the system pins.
In the CAPTURE-DR state, the Bypass register captures a logic 0.
In the SHIFT-DR state, test data shifts into the Bypass register on TDI, and
then after a delay of one TCK cycle, it shifts out on TDO. The first bit shifted
out is a 0.
The Bypass register is not affected by the UPDATE-DR state.
Note: All unused instruction codes default to the BYPASS instruction.
Table 9.1
Test Access Port Instruction Descriptions (Cont.)
Instruction
Description