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Notes
PES4T4 User Manual
®
Introduction
The JTAG Boundary Scan interface provides a way to test the interconnections between integrated
circuit pins after they have been assembled onto a circuit board. There are two pin types present in the
PES4T4: AC-coupled and DC-coupled (also called AC and DC pins). The Boundary Scan interface in the
PES4T4 is IEEE 1149.1 compliant to allow testing of the DC pins. The DC pins are those "normal" pins that
do not require AC-coupling.
The presence of AC-coupling capacitors on some of the PES4T4 pins prevents DC values from being
driven between a driver and receiver. An AC Boundary Scan methodology, as described in IEEE 1149.6, is
available to provide a time-varying signal to pass through the AC-coupling when in AC test mode; however,
IEEE 1149.6 is not supported in the PES4T4.
Test Access Point
The system logic utilizes a 16-state, TAP controller, a six-bit instruction register, and five dedicated pins
to perform a variety of functions. The primary use of the JTAG TAP Controller state machine is to allow the
five external JTAG control pins to control and access the PES4T4's many external signal pins. The JTAG
TAP Controller can also be used for identifying the device part number. The JTAG logic of the PES4T4 is
depicted in Figure 10.1.
Device ID Register
Bypass Register
Instruction Register Decoder
JTAG_TDI
4-Bit Instruction Register
JTAG_TMS
JTAG_TCK
JTAG_TRST_N
Refer to the IEEE 1149.1 and 1149.6 documents for a complete operational description of the Boundary
Scan and TAP controller.
Signal Definitions
JTAG operations such as reset, state-transition control, and clock sampling are handled through the
signals listed in Table 10.1. A functional overview of the TAP Controller and Boundary Scan registers is
provided in the sections following the table.
JTAG Boundary Scan
Boundary Scan Register
Tap Controller
Figure 10.1 Diagram of the JTAG Logic
10 - 1
Chapter 10
m
u
x
JTAG_TDO
m
u
x
February 1, 2011
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