Connections Between the Emulator and the Target System
15-9
Designing for JTAG Emulation
-
Buffered transmission signals. In this situation, the distance between
the emulation header and the processor is greater than six inches. Emula-
tion signals TMS, TDI, TDO, and TCK_RET are buffered through the same
package.
VCC
Emulator Header
VCC
GND
12
10
8
6
4
5
GND
GND
GND
GND
GND
PD
TCK_RET
TCK
TDO
TDI
TMS
TRST
EMU1
EMU0
9
11
7
3
1
2
14
13
JTAG Device
TCK
TDO
TDI
TMS
TRST
EMU1
EMU0
Greater Than
6 Inches
J
The EMU0 and EMU1 signals must have pullup resistors connected to
V
CC
to provide a signal rise time of less than 10
µ
s. A 4.7-k
Ω
resistor is
suggested for most applications.
J
The input buffers for TMS and TDI should have pullup resistors con-
nected to V
CC
to hold these signals at a known value when the emula-
tor is not connected. A resistor value of 4.7 k
Ω
or greater is suggested.
J
To have high-quality signals (especially the processor TCK and the
emulator TCK_RET signals), you may have to employ special care
when routing the PWB trace. You also may have to use termination
resistors to match the trace impedance. The emulator pod provides
optional internal parallel terminators on the TCK_RET and TDO. TMS
and TDI provide fixed series termination.
J
Since TRST is an asynchronous signal, it should be buffered as
needed to insure sufficient current to all target devices.