During uploading, the binary codes of a sketch are transmitted from PC to the target MCU (the Arduino) frame-by-frame. These frames are known as Intel-Hex formatted frames. Each frame could be viewed as one packet. There is no way to see extra packets except the last frame which the PC sends to mark the end-of-file.
Example:
void setup()
{
Serial.begin(9600);
Serial.print("Hello!");
}
void loop()
{
}
Before uploading, the above sketch is converted into the following frames. The frames are prepared from the object file which we can't see in the Arduino IDE (in MASM assembler of 80x86, we can see the object files). Each frame consists of 6 fields, and each field has its own meaning. Each and every symbol (say, :, 1, 0, ...) of the Intel-Hex frame is transmitted by the Virtual UART Port of the PC under asynchronous Protocol. In asynchronous data TX/RX Protocol, data are sent/received character-by-character called asynchronous data frame. Thus, : is sent as 00111010 (0x3A) which is an 8-bit ASCII code of :; 1 is sent as 00110001 (0x31) which is the ASCII code of 1, and so on. An asynchronous data frame is constructed by concatenating 1 start bit, 8 data bits, 1 parity bit (optional), and 1 stop bit.
:100000000C9435000C945D000C945D000C945D0024
:100010000C945D000C945D000C945D000C945D00EC
:100020000C945D000C945D000C945D000C945D00DC
:100030000C945D000C945D000C945D000C945D00CC
:100040000C9458010C945D000C94C8010C94A2010E
:100050000C945D000C945D000C945D000C945D00AC
:100060000C945D000C945D007D0211241FBECFEF47
:10007000D8E0DEBFCDBF11E0A0E0B1E0EEE6F5E0F4
:1000800002C005900D92A831B107D9F721E0A8E18F
:10009000B1E001C01D92AE3BB207E1F710E0C5E34D
:1000A000D0E004C02197FE010E94AA02C433D10708
:1000B000C9F70E94FA010C94B5020C940000CF928B
:1000C000DF92EF92FF920F931F93CF93DF936C0118
:1000D0007A018B01C0E0D0E0CE15DF0589F0D801B0
:1000E0006D918D01D601ED91FC910190F081E02D93
:1000F000C6010995892B11F47E0102C02196ECCF2F
:10010000C701DF91CF911F910F91FF90EF90DF908A
:10011000CF900895FC01918D828D981761F0828DAA
:10012000DF01A80FB11D5D968C91928D9F5F9F732B
:10013000928F90E008958FEF9FEF0895FC01918DCD
:10014000828D981731F0828DE80FF11D858D90E03A
:1001500008958FEF9FEF0895FC01918D228D892FD7
:1001600090E0805C9F4F821B91098F7399270895BF
:1001700088E191E00E94AC0021E0892B09F420E0A5
:10018000822F0895FC01848DDF01A80FB11DA35AB1
:10019000BF4F2C91848D90E001968F739927848FA7
:1001A000A689B7892C93A089B1898C9180648C939E
:1001B000938D848D981306C00288F389E02D808189
:1001C0008F7D80830895EF92FF920F931F93CF93BB
:1001D000DF93EC0181E0888F9B8D8C8D981305C097
:1001E000E889F989808185FD24C0F62E0B8D10E009
:1001F0000F5F1F4F0F731127E02E8C8DE8120CC07C
:100200000FB607FCFACFE889F989808185FFF5CF21
:10021000CE010E94C200F1CF8B8DFE01E80FF11DCF
:10022000E35AFF4FF0820B8FEA89FB89808180625D
:1002300007C0EE89FF896083E889F989808180643D
:10024000808381E090E0DF91CF911F910F91FF902B
:10025000EF900895CF93DF93EC01888D8823C9F048
:10026000EA89FB89808185FD05C0A889B9898C91BF
:1002700086FD0FC00FB607FCF5CF808185FFF2CF5A
:10028000A889B9898C9185FFEDCFCE010E94C2006B
:10029000E7CFDF91CF91089580E090E0892B29F09E
:1002A0000E94B80081110C94000008950E94B002D1
:1002B0001F920F920FB60F9211242F933F938F939B
:1002C0009F93AF93BF938091BA019091BB01A0918E
:1002D000BC01B091BD013091B90123E0230F2D374E
:1002E00020F40196A11DB11D05C026E8230F02963A
:1002F000A11DB11D2093B9018093BA019093BB0158
:10030000A093BC01B093BD018091B5019091B6015D
:10031000A091B701B091B8010196A11DB11D8093C4
:10032000B5019093B601A093B701B093B801BF9106
:10033000AF919F918F913F912F910F900FBE0F9092
:100340001F9018951F920F920FB60F9211242F93A2
:100350003F934F935F936F937F938F939F93AF934D
:10036000BF93EF93FF9388E191E00E94C200FF9159
:10037000EF91BF91AF919F918F917F916F915F911D
:100380004F913F912F910F900FBE0F901F90189596
:100390001F920F920FB60F9211242F938F939F935A
:1003A000EF93FF93E0912801F09129018081E09182
:1003B0002E01F0912F0182FD12C0908180913101B8
:1003C0008F5F8F7320913201821751F0E0913101DC
:1003D000F0E0E85EFE4F958F8093310101C080818F
:1003E000FF91EF919F918F912F910F900FBE0F90E2
:1003F0001F901895789484B5826084BD84B581601F
:1004000084BD85B5826085BD85B5816085BD8091DF
:100410006E00816080936E00109281008091810057
:10042000826080938100809181008160809381004F
:10043000809180008160809380008091B100846011
:100440008093B1008091B00081608093B000809172
:100450007A00846080937A0080917A008260809331
:100460007A0080917A00816080937A0080917A008E
:10047000806880937A001092C100E0912801F09189
:10048000290182E08083E0912401F091250110820E
:10049000E0912601F09127018FEC808310923001CA
:1004A000E0912C01F0912D0186E08083E0912A01FA
:1004B000F0912B01808180618083E0912A01F0918D
:1004C0002B01808188608083E0912A01F0912B01CB
:1004D000808180688083E0912A01F0912B018081E6
:1004E0008F7D808346E050E060E171E088E191E03B
:1004F0000E945F000E944C01FDCFE8E1F1E0138211
:10050000128288EE93E0A0E0B0E084839583A68316
:10051000B78384E091E09183808385EC90E09587B8
:10052000848784EC90E09787868780EC90E0918BBD
:10053000808B81EC90E0938B828B82EC90E0958BAA
:10054000848B86EC90E0978B868B118E128E138EA7
:10055000148E0895EE0FFF1F0590F491E02D09947D
:0E05600081E090E0F8940C94B502F894FFCF7F
:10056E0000000000E3005F00AC008A009E002A013C
:08057E0048656C6C6F21000060
:00000001FF