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IDT EJTAG System
Off-Chip and Probe Interfaces
79RC32438 User Reference Manual
20 - 76
November 4, 2002
Notes
Logical Signals
This section describes the EJTAG signals categorized according to functionality:
Test Access Port: JTAG_TCK, JTAG_TMS, JTAG_TDI, JTAG_TDO, and JTAG_TRST_N (optional)
System reset (reset or soft reset): RSTN
Voltage Sense for I/O: Vcc I/O.
Figure 20.38 shows the signal flow between the chip, target system PCB, and Probe.
Figure 20.38 Signal Flow Between Chip, Target System PCB, and Probe
Test Access Port Signals
The JTAG_TCK, EJTAG_TMS, JTAG_TDI, JTAG_TDO, and JTAG_TRST_N signals make up the Test
Access Port (TAP). For more details about the logical functionality of these signals, refer to section “EJTAG
Test Access Port” on page 20-54. These five signals are described in Table 20.53 below.
Signal
Description
Direction
Compliance
JTAG_TCK
Test Clock Input is the clock that controls the updates of
the TAP controller and the shifts through the Instruction or
selected data register(s). Both the rising and the falling
edges of JTAG_TCK are used.
Input
Required with
probe connection
EJTAG_TMS
Test Mode Select Input is the control signal for the TAP
controller. This signal is sampled at the rising edge of
JTAG_TCK.
Input
JTAG_TDI
Test Data Input has the data shifted into the Instruction or
data register. This signal is sampled on the rising edge of
JTAG_TCK
Input
JTAG_TDO
Test Data Output has the data shifted out from the Instruc-
tion or data register. This signal is changed on the falling
edge of JTAG_TCK.
Output
JTAG_TRST_N Test Reset Input is used for the TAP reset of the TAP con-
troller, Instruction register, and EJTAGBOOT indication.
TAP reset is applied asynchronously when low.
Input
Optional with probe
connection
Table 20.53 TAP Signals Overview
Target System
Reset Circuit
Probe
Connector
TCK
TMS
TDI
TDO
TRST*
RSTN
Vcc I/O
JTAG_TCK
EJTAG_TMS
JTAG_TDI
JTAG_TDO
JTAG_TRST_N
Chip with EJTAG
Reset
Other reset sources
(JTAG_TRST_N is optional, see description)
Chip I/O
Voltage
Target System
DINT
No connect