
Agere Systems Inc.
231
Data Sheet
July 2001
T8302 Internet Protocol Telephone
Advanced RISC Machine (
ARM
)
18 JTAG/Boundary Scan
Access to JTAG (joint test action group) and boundary-scan will be initially provided through a single set of JTAG
pins. The pin definitions are as follows:
I
Refer to the
ARM
940T documentation for additional information about JTAG and TAP controller signals.
18.1 Debug Support
Through the
ARM
940T JTAG interface and embedded ICE macrocell, the
ARM
development tools will provide the
user with the following hardware development capabilities:
I
Breakpointing on two watchpoints or breakpoints.
I
Single-stepping or step-by-N through code.
I
Inspection and modification of
ARM
accessible registers.
I
Inspection and modification of
ARM
memory.
I
Device reset through JTAG.
JTAG support is provided directly from the
ARM
940T core. Documentation for JTAG can be found in the
ARM
940T
technical reference.
Part number:
ARM
DDI 0144A.
18.2 The Principle of Boundary Scan Architecture
Each primary input signal and primary output signal is supplemented with a multipurpose memory element called
a boundary scan cell. Cells on device primary inputs are referred to as input cells and cells on primary outputs are
referred to as output cells. Input and output is relative to the core logic of the device.
At any time, only one register can be connected from JTDI to JTDO; for example, instruction register (IR), BYPASS,
boundary scan, IDENT, or even some appropriate register internal to the core logic; see
Figure 31
. The selected
register is identified by the decoded output of the instruction register. Certain instructions are mandatory, such as
EXTEST
(boundary scan register selected), whereas others are optional, such as the IDCODE
instruction (ident
register selected).
Table 207. Boundary Scan Pin Functions
Pin
P1
N3
P3
P2
R1
Boundary-Scan
JTRSTN (bscan)
JTDO (bscan)
JTCK (bscan)
JTMS (bscan)
JTDI (bscan)
Debug
JTRSTN (debug)
JTDO (debug)
JTCK (debug)
JTMS (debug)
JTDI (debug)
Debug mode, or boundary scan mode is selected via the JMODE pin (V18) as shown below.
Pin
V18
Name
JMODE
Description
When 0 = boundary scan.
When 1 = debug.