Introduction
1.7 Testability Design Methodology
Samsung ASIC
1-25
STDM110
Boundary Scan Functional Block Descriptions
TAP (Test Access Port)
TAP is a general-purpose port that can provide with an access to many test
support functions built into a component, including the test logic. It includes three
inputs (TCK; Test Clock Signal, TMS; Test Mode Signal and TDI; Test Data Input)
and one output (TDO; Test Data Output) required by the test logic. An optional
fourth input (TRSTN; Test Reset) is provided for the asynchronous initialization
of the test logic. The values applied at TMS and TDI pins are sampled on the
rising edge of TCK, and the value placed on TDO pin changes on the falling edge
of TCK.
TAP Controller
TAP controller receives TCK, interprets the signals on TMS, and generates clock
and control signals for both instruction and test data registers and for other parts
of the test circuitries as required.
Instruction Register/Instruction Decoder
Test instructions are shifted into and held by the instruction register. Test
instructions include a selection of tests to be performed or the test data register
to be accessed. A basic 3-bit instruction register and its instruction decoder are
provided as macrofunctions in the library.
Test Data Registers
Data registers include a bypass register, a boundary scan register, a device
identification register and other design specific registers. Only the bypass- and
boundary scan registers are mandatory; the rest are optional.
Bypass register: The bypass register provides a single-bit serial connection through
the circuit when none of the other test data registers is selected. It
can be used to allow test data to flow through a given device to the
other components in a product without affecting a normal operation.
Boundary scan register: The boundary scan register detects typical production defects in
board interconnects, such as opens, shorts, etc. It also allows an
access to component inputs and outputs when you test their logic or
sample flow-through signals. Special boundary scan register
macrocells are provided for this purpose. These special registers is
discussed in the next section of next pages.
Design-specific test data register: These optional registers may be provided to allow an access to
design-specific test support features in the integrated circuit, such as
self-test, scan test.
Device identification register: This is an optional test data register that allows the manufacturer part
number and variant of a components to be identified. The 32-bit
identification register is partitioned into four fields:
Device version identifier1st field
Device part number
Manufacturer’s JEDEC number
LSB
The first four bits beginning from MSB
2nd field
16 bits
3rd field
11 bits
4th field
1 bit —tied in High