Microchip Technology Power Debugger Manual page 75

• Try to add or remove a small number of breakpoints at a time, to minimize the number of FLASH page write
operations
• If possible, avoid placing breakpoints on double-word instructions
4.4.16 Understanding debugWIRE and the DWEN Fuse
When enabled, the debugWIRE interface takes control of the device's /RESET pin, which makes it mutually exclusive
to the SPI interface, which also needs this pin. When enabling and disabling the debugWIRE module, follow one of
these two approaches:
• Let the software front-end take care of things (recommended)
• Set and clear DWEN manually (exercise caution, advanced users only!)
Important: When manipulating DWEN manually, it is important that the SPIEN fuse remains set to avoid
having to use High-Voltage programming.
Figure 4-14. Understanding debugWIRE and the DWEN Fuse
Start debug session
Atmel Studio "Disable debugWIRE and close"
(disables debugWIRE module temporarily
and then clears DWEN fuse using SPI)
MPLAB X IDE offers to do this automatically
if an attempt to connect using the SPI interface
fails due to debugWIRE being enabled
4.4.17 TinyX-OCD (UPDI) Special Considerations
The UPDI data pin (UPDI_DATA) can be a dedicated pin or a shared pin, depending on the target AVR device. A
shared UPDI pin is 12V tolerant, and can be configured to be used as /RESET or GPIO. For further details on how to
use the pin in these configurations, see
On devices which include the CRCSCAN module (Cyclic Redundancy Check Memory Scan), this module should not
be used in Continuous Background mode while debugging. The OCD module has limited hardware breakpoint
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2020 Microchip Technology Inc.
Default state:
Fuse DWEN cleared
Fuse SPIEN set
Module debugWIRE disabled
You can: Access flash and fuses using SPI
Intermediate state 1:
Fuse DWEN set
Fuse SPIEN set* (NB!)
Module debugWIRE disabled until power toggle
You can: Toggle power
Power toggle
(latches debugWIRE state)
Debug state:
Fuse DWEN set
Fuse SPIEN set
Module debugWIRE enabled
You can: use debugWIRE
You cannot: Access fuses or flash using SPI
4.4.7 UPDI Physical
DWEN
SPIEN
Clear DWEN fuse
using SPI
Set DWEN fuse
using SPI
DWEN Intermediate state 2:
Fuse DWEN set
SPIEN
Fuse SPIEN set
Module debugWIRE disabled
You can: Access fuses and flash using SPI
DWEN
SPIEN
atprogram dwdisable
Debug state (not recommended):
Fuse DWEN set
Fuse SPIEN cleared
Module debugWIRE enabled
You can: use debugWIRE
To access flash and fuses it is now necessary to
use the High-Voltage Programming interface
Interface.
User Guide
Power Debugger
On-chip Debugging
DWEN
SPIEN
(atprogram disables
debugWIRE module temporarily)
DWEN
SPIEN
DS40002201A-page 75