MMC2001
OnCE™ DEBUG MODULE
MOTOROLA
REFERENCE MANUAL
16-1
SECTION 16
OnCE™ DEBUG MODULE
16.1 Overview
The on-chip emulation (OnCE™) circuitry provides a simple, inexpensive debugging
interface that allows external access to the processor’s internal registers and to mem-
ory/peripherals. OnCE capabilities are controlled through a serial interface, mapped
onto a JTAG test access port (TAP) protocol. Figure 16-1 shows the components of
the OnCE circuitry.
Figure 16-1 OnCE Block Diagram
The interface to the OnCE controller and its resources is based on the TAP defined
for JTAG in the IEEE-1149.1a-1993 standard.
16.2 Operation
An instruction is scanned into the OnCE module through the serial interface and then
decoded. Data may then be scanned in and used to update a register or resource on
a write to the resource, or data associated with a resource may be scanned out for a
read of the resource.
PSTAT
ATTR
ADDR
.
.
.
TDO
TMS
TDI
TCK
Breakpoint and
Trace Logic
OnCE
Controller
and
Serial
Interface
Breakpoint
Registers
and
Comparators
PC
FIFO
Pipeline
Information
TRST
BRKRQ
DBGRQ
DEBUG
DBGACK
IDR
DE
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I
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