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IDT JTAG Boundary Scan
Test Data Register (DR)
79RC32438 User Reference Manual
19 - 3
November 4, 2002
Notes
JTAG_TCK. A state diagram for the TAP controller appears in Figure 19.3. The value next to state repre-
sent the value that must be applied to JTAG_TMS on the next rising edge of JTAG_TCK, to transition in the
direction of the associated arrow.
Figure 19.3 State Diagram of RC32438’s TAP Controller
Test Data Register (DR)
The Test Data register contains the following:
The Bypass register
The Boundary Scan registers
The Device ID register
These registers are connected in parallel between a common serial input and a common serial data
output, and are described in the following sections. For more detailed descriptions, refer to IEEE Standard
Test Access port (IEEE Std. 1149.1-1990).
Boundary Scan Registers
The RC32438 scan chain is 489 bits long and comprises 259 logical elements — where each logical
element represents a signal pin. The five JTAG pins do not have scan elements associated with them, nor
does the EJTAG EJTAG_TMS pin. In addition, DDRVREF and PLLTEST do not have scan elements asso-
ciated with them. Of the 259 logical elements, 141 are two-bit bidirectional cells, 89 are two-bit tri-statable
outputs, and 29 are one-bit dedicated inputs.
This boundary scan chain is connected between JTAG_TDI and JTAG_TDO when the EXTEST or
SAMPLE/PRELOAD instructions are selected. Once EXTEST is selected and the TAP controller passes
through the UPDATE-IR state, whatever value is currently held in the boundary scan register’s output
latches is immediately transferred to the corresponding outputs or output enables.
Test- Logic
Reset
Run-Test/
Idle
Select-
DR-Scan
Capture-DR
Shift-DR
Exit1 -DR
Pause-DR
Exit2-DR
Select-
IR-Scan
Capture-IR
Shift-IR
Exit1-IR
Pause-IR
Exit2-IR
Update-DR
Update-IR
1
1
0
0
0
1
1
0
0
1
1
0
1
0
1
0
0
1
1
1
0
0
1
1
0
1
0
1
1
0
0
0
0