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Chapter 2. Functions
2.3 Emulation Operation
Emulation involves running a user application program, under the control of software on a development
host, in real time at the same speed and with electrical characteristics approaching those of the volume
production masked ROM version. These last two characteristics distinguish it from simulation, the
replacement of hardware with software running on a development host.
Two types of emulation are available: real-time and single-step. The former runs nonstop up until a
break. The latter pauses after each instruction to permit such debugging operations as examining and
modifying register contents.
Control from the host is possible because the evaluation chip inside the emulator has no masked ROM.
Instead there are data and address buses to RAM and other external devices plus related control
circuits. These modifications permit the microcontroller to execute the user application program in real
time while still allowing the emulator (as thus the control software) debugging access to the device's
memory, registers, and flags. The microcontroller uses this additional hardware to read instructions; the
emulator, to control user application program execution and access these internal device components.
The pins that the evaluation chip shares with the volume production masked ROM version are
connected to the user application system through the user cables.
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n Note 1 n
The circuits that correspond to the ML63512/514 for the Dr.63514 in-circuit emulator consist of
the nX-4/250 core evaluation chip, which corresponds to the ML63512/514 CPU core block,
and a block that corresponds to the ML63512/514 I/O block. Note that since the I/O block is
formed from normal discrete components, the electrical characteristics of the ports and other
circuits differ somewhat from those of the ML63512/514. See chapter 4, "Additional Usage
Notes", for details on these differences.
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2.3.1 Single-Step Emulation
Single-step emulation pauses after each instruction to permit such debugging operations as examining
and modifying register contents.
<During single-step emulation>
• Emulation aborts if the program counter (PC) strays into the nonexistent code memory area (N area).
• HALT is just another instruction. It produces a temporary transition to halt mode followed by an
immediate return.
• Real-time tracing and the cycle counter are disabled.
2-8
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