
MOTOROLA
OnCE™ DEBUG MODULE
MMC2001
16-4
REFERENCE MANUAL
16.3.5 Test Reset (TRST)
The test reset input is used to reset the OnCE controller externally by placing the
OnCE control logic in a test logic reset state. OnCE operation is disabled in the reset
controller and reserved states.
16.3.6 Debug Event (DE)
The debug event (DE) pin is a bidirectional open drain pin. As an input, DE provides a
fast means of entering debug mode from an external command controller. As an out-
put, this pin provides a fast means of acknowledging debug mode entry to an external
command controller.
The assertion of this pin by a command controller causes the CPU to finish the cur-
rent instruction being executed, save the instruction pipeline information, enter debug
mode, and wait for commands to be entered from the TDI line. If DE was used to
enter debug mode, then DE must be negated after the OnCE responds with an
acknowledgment and before sending the first OnCE command.
The assertion of this pin by the CPU acknowledges that it has entered debug mode
and is waiting for commands to be entered from the TDI line.
16.4 OnCE Controller and Serial Interface
Figure 16-3 is a block diagram of the OnCE controller and serial interface.
Figure 16-3 OnCE Controller and Serial Interface
OnCE Command Register
TDI
TCK
Status and Control
Registers
TDO
Mode Select
OnCE Decoder
ISBKPT
ISDR
ISTRACE
Register Write
Register Read
.
.
.
.
.
TAP
TMS
CPU Control/Status
Controller
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