
DS3112
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SAMPLE/PRELOAD
A mandatory instruction for the IEEE 1149.1 specification that supports two functions. The digital I/Os of
the DS3112 can be sampled at the Boundary Scan register without interfering with the normal operation
of the device by using the Capture-DR state. SAMPLE/PRELOAD also allows the DS3112 to shift data
into the Boundary Scan register via JTDI using the Shift-DR state.
EXTEST
EXTEST allows testing of all interconnections to the DS3112. When the EXTEST instruction is latched
in the instruction register, the following actions occur. Once enabled via the Update-IR state, the parallel
outputs of all digital output pins will be driven. The Boundary Scan register will be connected between
JTDI and JTDO. The Capture-DR will sample all digital inputs into the Boundary Scan register.
BYPASS
When the BYPASS instruction is latched into the parallel Instruction register, JTDI connects to JTDO
through the one-bit Bypass Test register. This allows data to pass from JTDI to JTDO not affecting the
device's normal operation.
IDCODE
When the IDCODE instruction is latched into the parallel Instruction register, the Identification Test
register is selected. The device identification code will be loaded into the Identification register on the
rising edge of JTCLK following entry into the Capture-DR state. Shift-DR can be used to shift the
identification code out serially via JTDO. During Test-Logic-Reset, the identification code is forced into
the instruction register's parallel output. The device ID code will always have a one in the LSB position.
The next 11 bits identify the manufacturer’s JEDEC number and number of continuation bytes followed
by 16 bits for the device and 4 bits for the version. The device ID code for the DS3112 is
0000B143h
.
HIGH-Z
All digital outputs will be placed into a high impedance state. The Bypass Register will be connected
between JTDI and JTDO.
CLAMP
All digital outputs will output data from the boundary scan parallel output while connecting the Bypass
Register between JTDI and JTDO. The outputs will not change during the CLAMP instruction.
11.4 Test Registers
IEEE 1149.1 requires a minimum of two test registers, the bypass register and the boundary scan register.
An optional test register, the Identification register, has been included in the DS3112 design. It is used in
conjunction with the IDCODE instruction and the Test-Logic-Reset state of the TAP controller.
Bypass Register
This is a single one-bit shift register used in conjunction with the BYPASS, CLAMP, and HIGH-Z
instructions that provides a short path between JTDI and JTDO.
Identification Register
The Identification register contains a 32-bit shift register and a 32-bit latched parallel output. This register
is selected during the IDCODE instruction and when the TAP controller is in the Test-Logic-Reset state.