I tell you what! You're the key to unlocking every mystery I come across in these card reader emulator projects!
reader in ID4 looks like natural evolution of previous one - 8byte SN# and password, 8x 16bit counters instead of 4x 8bit, etc but in general it is same thing, which works using same basic principle and commands.
so the key is - research for understanding how things works, but not just blindly supply games with some void/unk data bytes to make them happy
I'm curious though how you read the CMD variable and get the address from it? Like how does C0 translate to x30-x31, 30 translates to x32-x33, etc?
6D 00 C0 -> C0 00 -> 11000000 00000000 = counter # 0 (ie offset 30h)
6D 00 03 -> 03 00 -> 00000011 00000000 = counter # 3 (ie offset 36h)
6D 03 00 -> 00 03 -> 00000000 00000011 = counter # 7 (ie offset 3Eh)