IDT JTAG Boundary Scan
System Logic TAP Controller Overview
79RC32438 User Reference Manual
19 - 2
November 4, 2002
Notes
System Logic TAP Controller Overview
The system logic utilizes a 16-state, six-bit TAP controller, a four-bit instruction register, and five dedi-
cated 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 RC32438's many external signal pins.
The JTAG TAP Controller can also be used for identifying the device part number. The JTAG logic of the
RC32438 is depicted in Figure 19.2.
Figure 19.2 Diagram of the JTAG Logic
Signal Definitions
JTAG operations such as Reset, State-transition control and Clock sampling are handled through the
signals listed in Table 19.1. A functional overview on the TAP Controller and Boundary Scan registers is
provided in the sections following the table.
The system logic TAP controller transitions from state to state, according to the value present on
JTAG_TMS, as sampled on the rising edge of JTAG_TCK. The Test-Logic Reset state can be reached
either by asserting JTAG_TRST_N or by applying a 1 to JTAG_TMS for five consecutive cycles of
Pin Name
Type
Description
JTAG_TRST_N
Input
JTAG RESET
Asynchronous reset for JTAG TAP controller (internal pull-up)
JTAG_TCK
Input
JTAG Clock
Test logic clock. Jtag_tms and jtag_tdi are sampled on the rising edge. Jtag_tdo is output
on the falling edge.
JTAG_TMS
Input
JTAG Mode Select Requires an external pull-up.
Controls the state transitions for the TAP controller state machine (internal pull-up)
JTAG_TDI
Input
JTAG Input
Serial data input for BSC chain, Instruction Register, IDCODE register, and BYPASS
register (internal pull-up)
JTAG_TDO
Output JTAG Output
Serial data out. Tri-stated except when shifting while in Shift-DR and SHIFT-IR TAP con-
troller states.
Table 19.1 JTAG Pin Descriptions
Bypass Register
Instruction Register Decoder
4-Bit Instruction Register
Tap Controller
m
u
x
m
u
x
Device ID Register
Boundary Scan Register
JTAG_TDI
JTAG_TMS
JTAG_TCK
JTAG_TRST_N
JTAG_TDO