EverFocus EDR-920 - Manual (Page 148)

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0x1f JOG> 0x2c SELECT
0x20 CH5 0x2d CALL
0x21 CH6 0x2e ENTER
0x22 CH7 0x2f (reserved)
0x23 CH8 0x30 (reserved)
0x24 CH9 0x31 (reserved)
0x25 CH 10 0x32 (reserved)
0x26 CH 11 0x33 (reserved)
0x27 CH 12 0x34 (reserved)
0x28 CH 13
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2-5. Checksum Byte
Checksum is computed as the sum of all previous bytes (including the length byte), then mask with 0x7f.