Epson ARM.POWERED ARM720T - Manual (Page 140)

9: Debugging Your System
9-8 EPSON ARM720T CORE CPU MANUAL
9.3.5 Clocks
The system and test clocks must be synchronized externally to the processor. The ARM
Multi-ICE debug agent directly supports one or more cores within an ASIC design.
Synchronizing off-chip debug clocking with the ARM720T processor requires a three-stage
synchronizer. The off-chip device (for example, Multi-ICE) issues a TCK signal and waits for
the RTCK (Returned TCK) signal to come back. Synchronization is maintained because the
off-chip device does not progress to the next TCK until after RTCK is received.
Figure 9-4 shows this synchronization.
Figure 9-4 Clock synchronization
Note:
All the D-types shown in Figure 9-4 are reset by DBGnTRST.
Reset circuit
DBGnTRST nTRST
DBGTDO TDO
D Q D Q D Q
HCLK
TCK synchronizer
TCK
RTCK
D Q
EN
TMS
D Q
EN
Input sample
and hold
HCLK
HCLK
HCLK
TDI
DBGTMS
DBGTDI
A
R
M7
T
D
MI
-S
ma
cr
o
c
e
ll
Multi_ICE interface pads
DBGTCKEN