Connections Between the Emulator and the Target System
15-11
Designing for JTAG Emulation
15.7.3 Configuring Multiple Processors
Figure 15–5 shows a typical daisy-chained multiprocessor configuration,
which meets the minimum requirements of the IEEE 1149.1 specification. The
emulation signals in this example are buffered to isolate the processors from
the emulator and provide adequate signal drive for the target system. One of
the benefits of this type of interface is that you can generally slow down the test
clock to eliminate timing problems. You should follow these guidelines for
multiprocessor support:
-
The processor TMS, TDI, TDO, and TCK signals should be buffered
through the same physical package for better control of timing skew.
-
The input buffers for TMS, TDI, and TCK should have pullup resistors con-
nected to V
CC
to hold these signals at a known value when the emulator
is not connected. A resistor value of 4.7 k
Ω
or greater is suggested.
-
Buffering EMU0 and EMU1 is optional but highly recommended to provide
isolation. These are not critical signals and do not have to be buffered
through the same physical package as TMS, TCK, TDI, and TDO. Unbuf-
fered and buffered signals are shown in this section (page 15-8 and page
15-9).
Figure 15–5. Multiprocessor Connections
TDI
TDI
TDO
TDO
JTAG Device
JTAG Device
VCC
Emulator Header
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
TMS
TCK
TRST
EMU0
EMU1
TMS
TCK
TRST
EMU0
EMU1
VCC