Atmel AVR ICE 200, User Manual

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AVR ICE 200 User Guide 5-1
Section 5
Special Considerations
The ICE 200 accurately emulates most AVR features. However, there are some differ-
ences worth noting. Most of the exceptions apply to controlling the program flow, i.e.
single-stepping and so on. Program flow control is an extension to the normal functions
of the microcontroller that allows the user to do the debugging. This extension must not
interfere with the normal program execution (run mode). If the program execution is
stopped (stopped mode) and then restarted, or the program is executed line-by-line
(single-stepping), the program functionality can, in some cases, be affected.
5.1 External RESET
The ICE 200 main board has to be able to control the reset pin on the AVR emulator
chip. An external reset source must therefore go via the control logic as shown
on Figure 5-1. This is handled automatically by the pod and main board
Figure 5-1. ICE 200, External RESET Circuit
The main board is working with 5V supply and the pod uses the target voltage.
Therefore, a level converter is inserted between the two systems. The extra logic and
the level converters introduce a small, and for most of the time, negligible delay. Note
that the voltage converters do not handle a +12V input voltage on the RESET pin which
is used for enabling the parallel programming on standard parts.
After a power-up, the reset is forced active while configuring the AVR emulator chip,
introducing a 1 - 10 ms delay.
POD MAIN BOARD
Voltage Level Converter
FORCE RESET
ENABLE RESET
RESET
External RESET