Emulation Timing Calculations
15-7
Designing for JTAG Emulation
Case 2:
Single/multiprocessor, TMS/TDI/TCK buffered input, TDO buffered output,
TMS/TDI timed from TCK_RET low.
t
pd (TCK_RET–TMS
ń
TDI)
+
ƪ
t
d (TMSmax
)
)
t
su (TTMS
)
)
t
(bufskew)
ƫ
t
ǒ
TCKfactor
Ǔ
+
ƪ
20ns
)
10 ns
)
1.35 ns
ƫ
0.4
+
78.4ns (12.7 MHz)
t
pd (TCK_RET–TDO)
+
ƪ
t
d (TTDO
)
)
t
su (TDOmin)
)
t
d (bufmax
)
ƫ
t
ǒ
TCKfactor
Ǔ
+
70ns (14.3 MHz)
+
[15ns
)
3ns
)
10ns]
0.4
In this case, the TCK_RET-to-TMS/TDI path is the limiting factor.
In a multiprocessor application, it is necessary to ensure that the EMU0–1 lines
can go from a logic low level to a logic high level in less than 10
µ
s. This can be
calculated as follows:
t
r
= 5(R
pullup
×
N
devices
×
C
load_per_device
)
= 5(4.7 k
W
×
16
×
15 pF)
= 5.64
µ
s