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[jim121049]

I'm trying to communicate with the embedded controller in a piece of equipment over a serial link. Below are some examples of the data (hexadecimal bytes) sent between the PC and controller:

Each line represents a complete message. The first byte (0x81) on each line indicates the start of a message. The second byte indicates the number of bytes in the message. The bytes that follow are parameters. The last byte on each line is a checksum (supposedly a 1's complement checksum). Try as I may, I can't figure out how the checksum is calculated. Any ideas on how the checksum is computed?
Thanks in advance.

81 08 A8 0F 00 02 00 02 00 AF
81 08 A8 0F 00 03 00 02 00 AE
81 08 A8 0F 00 04 00 02 00 B1
81 08 A8 0F 00 05 00 02 00 B0
81 08 A8 0F 00 1D 00 02 00 B8
81 08 A8 0F 00 1E 00 02 00 B3
81 08 A8 0F 00 1F 00 02 00 B2
81 08 A8 0F 00 20 00 02 00 95
81 08 A8 0F 00 21 00 02 00 94
81 08 A8 0F 00 22 00 02 00 8F
81 07 F8 11 01 00 00 00 E4
81 07 F8 11 02 00 00 00 E7
81 07 F8 11 04 00 00 00 E9
81 07 76 07 00 00 80 3F C4
81 04 4C 04 00 50
81 04 90 01 00 99
81 03 52 12 46
81 03 90 01 95