Debug Interface
7-4
Table 7−1. 14-Pin Header Signal Descriptions
Signal Description
Emulator
State
†
Target
State
†
EMU0 Emulation pin 0 I I/O
EMU1 Emulation pin 1 I I/O
GND Ground
PD (V
CC
) Presence detect. Indicates that the emulation
cable is connected and that the target is pow-
ered up. PD should be tied to V
CC
in the target
system.
IO
TCK Test clock. TCK is a clock source from the
emulation cable pod. This signal can be used
to drive the system test clock.
OI
TCK_RET Test clock return. Test clock input to the emu-
lator. Can be a buffered or unbuffered version
of TCK.
IO
TDI Test data input O I
TDO Test data output I O
TMS Test mode select O I
TRST
‡
Test reset O I
†
I = input; O = output
‡
Do not use pullup resistors on TRST: it has an internal pulldown device. In a low-noise
environment, TRST can be left floating. In a high-noise environment, an additional pulldown
resistor may be needed. (The size of this resistor should be based on electrical current
considerations.)
The state of the TRST, EMU0, and EMU1 signals at device power up deter-
mine the operating mode of the device. The operating mode takes effect as
soon as the device has sufficient power to operate. Should the TRST signal
rise, the EMU0 and EMU1 signals are sampled on its rising edge and the\at
operating mode is latched. Some of these modes are reserved for test pur-
poses, but those that can be of use in a target system are detailed in Table 7−2.
A target system is not required to support any mode other than normal mode.
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