Pokedex
In the newer games, you have two Pokedexes: A Johto Pokedex, which you use throughout the majority of the game and which allows data for only 151 Pokemon, and a National Pokedex, which you obtain after you complete the game and which allows you to obtain data on all 493 Pokemon that are obtainable in "Pokemon HeartGold" and "Pokemon SoulSilver." There are different codes for completing both Pokedexes.
Using Your Action Replay
To use your Nintendo DS Action Replay, insert your "Pokemon" game into the Action Replay and then insert the Action Replay itself into the Nintendo DS as if it were a game card. The Action Replay has a cartridge slot so that you can connect the game to it. Once the Action Replay is properly connected, you can turn the system on and begin inputting codes you wish to enable.
Johto Pokedex
At the code screen of the Action Replay, input the following code:
94000130 FFFB0000
62110DC0 00000000
B2110DC0 00000000
000015FC 00010101
00001560 FFFCC750
10001564 0000FDFE
00001308 10001FFF
C0000000 0000000E
000012CC FFFFFFFF
DC000000 00000004
D2000000 00000000
94000130 FFFB0000
62110DC0 00000000
B2110DC0 00000000
C0000000 0000000E
0000130C FFFFFFFF
DC000000 00000004
D2000000 00000000
94000130 FFFB0000
62110DC0 00000000
B2110DC0 00000000
E0001348 000000A8
32001FFF 70000000
00000000 00000000
08050000 00000000
00000000 00000000
00032000 00000000
02000000 00000000
08000000 90000000
00800000 20000000
00000080 7FFFFFFF
FFFFFFFC FFFCFFFF
7E7FF9E7 FF9C7EF7
FFFFFFFF FFFFFEFF
F8E3E6FF FFFFFFFF
FEFFFFF7 FF3CFFFF
081FFFFF DFFFFFFC
FFE7FFFF 39FFDFFF
00000090 A2AC83FB
E4E4FEFE 03020100
07060504 0B0A0908
0F0E0D0C 13121110
17161514 1B1A1918
D2000000 00000000
94000130 FFFB0000
62110DC0 00000000
B2110DC0 00000000
C0000000 000001EC
2000140D 0000003F
DC000000 00000001
D2000000 00000000
Press "Start" to begin playing your "Pokemon" game. Once you start the game, you will have all 151 Pokemon in the Johto Pokedex.
National Pokedex
Using the code for the National Pokedex is the same process as before, but with a different code. The code for the complete National Pokedex is as follows:
1206EA8A 00004800
0206EA8C 023C0001
1206EA90 00004700
E23C0000 00000010
3E404802 46C061B0
BDF8B014 000FFFFF
94000130 FFFB0000
62110DC0 00000000
B2110DC0 00000000
000015FC 01010101
00001560 FFFCC750
10001564 0000FDFE
00001308 10001FFF
C0000000 0000000E
000012CC FFFFFFFF
DC000000 00000004
D2000000 00000000
94000130 FFFB0000
62110DC0 00000000
B2110DC0 00000000
C0000000 0000000E
0000130C FFFFFFFF
DC000000 00000004
D2000000 00000000
94000130 FFFB0000
62110DC0 00000000
B2110DC0 00000000
E0001348 000000A8
32001FFF 70000000
00000000 00000000
08050000 00000000
00000000 00000000
00032000 00000000
02000000 00000000
08000000 90000000
00800000 20000000
00000080 7FFFFFFF
FFFFFFFC FFFCFFFF
7E7FF9E7 FF9C7EF7
FFFFFFFF FFFFFEFF
F8E3E6FF FFFFFFFF
FEFFFFF7 FF3CFFFF
081FFFFF DFFFFFFC
FFE7FFFF 39FFDFFF
00000090 A2AC83FB
E4E4FEFE 03020100
07060504 0B0A0908
0F0E0D0C 13121110
17161514 1B1A1918
D2000000 00000000
94000130 FFFB0000
62110DC0 00000000
B2110DC0 00000000
C0000000 000001EC
2000140D 0000003F
DC000000 00000001
D2000000 00000000
With the code in place, start the game and you will have the data for all 493 obtainable Pokemon.
Warnings
Do not use both codes at the same time as it can corrupt your data or even potentially erase your game file. Additionally, using these codes will make your game ineligible for use in any official "Pokemon" tournament sponsored by Nintendo.