Multi-master Systems and Arbitration............................................................... 226
Analog Comparator ......................................................................... 228
Analog Comparator Multiplexed Input .............................................................. 230
Analog-to-Digital Converter............................................................ 231
Features............................................................................................................ 231
Starting a Conversion ....................................................................................... 233
Prescaling and Conversion Timing................................................................... 234
Changing Channel or Reference Selection ...................................................... 236
ADC Noise Canceler......................................................................................... 237
ADC Conversion Result.................................................................................... 241
debugWIRE On-chip Debug System.............................................. 246
Features............................................................................................................ 246
Overview........................................................................................................... 246
Physical Interface ............................................................................................. 246
Software Break Points ...................................................................................... 247
Limitations of debugWIRE ................................................................................ 247
debugWIRE Related Register in I/O Memory................................................... 247
Self-Programming the Flash, ATmega48....................................... 248
Addressing the Flash During Self-Programming .............................................. 249
Boot Loader Support – Read-While-Write Self-Programming,
ATmega88 and ATmega168............................................................ 255
Boot Loader Features....................................................................................... 255
Application and Boot Loader Flash Sections.................................................... 255
Read-While-Write and No Read-While-Write Flash Sections........................... 255
Boot Loader Lock Bits....................................................................................... 258
Entering the Boot Loader Program................................................................... 259
Addressing the Flash During Self-Programming .............................................. 261
Self-Programming the Flash............................................................................. 262
Memory Programming..................................................................... 270
Program And Data Memory Lock Bits .............................................................. 270
Fuse Bits........................................................................................................... 272
Signature Bytes ................................................................................................ 274
Calibration Byte ................................................................................................ 274
Page Size ......................................................................................................... 274
Parallel Programming Parameters, Pin Mapping, and Commands .................. 275
Serial Programming Pin Mapping..................................................................... 277
Parallel Programming ....................................................................................... 278
Serial Downloading........................................................................................... 286
Electrical Characteristics................................................................ 290
iv
ATmega48/88/168
2545D–AVR–07/04