Table of Contents
Advertisement
Chapter 4: Connecting the Emulator to a Target System
Plugging The Emulator Into A Target System
specifications in mind while you design your target system, you can save hours of
debugging time when you plug the emulator into your target system.
Buffering and AC specifications
Most signals going to and from the emulator are not intercepted. Of those that are,
for example the data bus, nearly all are gated using analog transmission gates,
which introduce very little delay in these signals. Because these gates don't buffer
the signal when they are on, the target system and the internal signals of the
emulator are effectively connected. This typically results in the target system
seeing more capacitance because of emulator circuitry and traces than with the
processor alone. The net result is that even though these transmission gates don't
add a lump sum delay, the capacitance may slow the edges of the signal, resulting
in an extra delay.
The CLKOUT signal is buffered with an FCTA family part, followed by circuitry
to allow operation at 3.3 volts. This improves drive capability to the target system
and signal quality to the emulator.
DC specifications
Examine the DC specifications of the emulator to evaluate their differences from
processor specifications. Again, you can refer to the equivalent circuit diagrams in
this chapter for exact details. Because the emulator does not behave exactly like
the processor, you may need to examine signal quality and take appropriate steps to
compensate for differences.
Clocks
The MC6833x can operate in two basic clock modes: clocked from an oscillator, or
clocked from a crystal. The emulator supports both these modes. To provide the
most flexibility for supporting these clock modes, the emulator allows operation
from either the target system clock source (external) or from an internal clock
source.
The CLKOUT clock is the most important signal to the emulator because all
system timing is derived from the CLKOUT signal. For proper operation, the
CLKOUT clock signal must always be available to the emulator. It is possible to
turn off the CLKOUT signal by setting the EXOFF bit in the SIM (or SCIM)
Module Configuration Register (MCR). Make certain your target program never
sets EXOFF.
51
Advertisement
Table of Contents
