Emulation Design Considerations
15-17
Designing for JTAG Emulation
Of the following two cases, the worst-case path delay is calculated to deter-
mine the maximum system test clock frequency.
Case 1:
Single processor, direct connection, DTMS/DTDO timed from TCK low.
t
pd
ǒ
TCK–DTMS
Ǔ
+
ƪ
t
d
ǒ
DTMSmax
Ǔ
)
t
d
ǒ
DTCKHmin
Ǔ
)
t
su
ǒ
TTMS
Ǔ
ƫ
t
ǒ
TCKfactor
Ǔ
+
[31ns
)
2ns
)
10ns]
0.4
+
107.5ns (9.3 MHz)
t
pd
ǒ
TCK–DTDI
Ǔ
+
ƪ
t
d
ǒ
TTDO
Ǔ
)
t
d
ǒ
DTCKLmax
Ǔ
)
t
su
ǒ
DTDLmin
Ǔ
ƫ
t
ǒ
TCKfactor
Ǔ
+
[15ns
)
16ns
)
7ns]
0.4
+
9.5ns (10.5 MHz)
In this case, the TCK-to-DTMS/DTDL path is the limiting factor.
Case 2:
Single/multiprocessor, DTMS/DTDO/TCK buffered input, DTDI buffered out-
put, DTMS/DTDO timed from TCK low.
t
pd (TCK–TDMS)
+
ƪ
t
d (DTMSmax)
)
t
ǒ
DTCKHmin
Ǔ
)
t
su (TTMS)
)
t
(bufskew)
ƫ
t
ǒ
TCKfactor
Ǔ
+
[31ns
)
2ns
)
10ns
)
1.35ns]
0.4
+
110.9ns (9.0 MHz)
t
pd (TCK–DTDI)
+
ƪ
t
d (TTDO)
)
t
d
ǒ
DTCKLmax
Ǔ
)
t
su (DTDLmin
)
)
t
d (bufskew)
t
ǒ
TCKfactor
Ǔ
+
120ns (8.3 MHz)
+
[15ns
)
15ns
)
7ns
)
10ns]
0.4
In this case, the TCK-to-DTDI path is the limiting factor.