5 - 4 SE4750 Integration Guide
Command Checksum
Every command must include a checksum, calculated as follows:
1. Sum the bytes in the command, starting from the opcode through the last command data byte.
2. Use only the low byte of this result.
3. Perform a 2's complement of this result.
This value is the checksum and is added to the checksum field of the command.
Response Status Code
Every response includes a status code that indicates the success of the command. A successful command returns
an ACK or 0x80.
Table 5-2 lists status codes for single errors. Note that these error codes are bit positions within the status byte,
and two errors can occur (e.g., NAK and AIM_POWER_FAIL), resulting in values not listed in this table.
Table 5-2
Response Status Codes
Status Value Cause / Meaning
ACK 0x80 Command was successful.
NAK 0x82 (Bit 1 set) Command failed. Possible causes are:
•
Invalid opcode
•
Invalid command format
•
Invalid parameter value
CKSM_ERR 0x84 (Bit 2 set) The transmitted checksum did not match the checksum of the
data.
AIM_POWER_FAILURE 0x88 (Bit 3 set) The aiming power exceeded its limit.
THERMAL_FAILURE 0x90 (Bit 4 set) The internal temperature exceeded its limit.
INTERNAL_I2C_FAILURE 0xA0 (Bit 5 set)
The internal I
2
C interface failed.
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