MegaPlus ES 1020
User’s Manual
Redlake MASD, Inc.
Page
13
91000134-001 Rev. A
Check
Data Checksum - calculated on DATA Only
Size = 2 ascii characters - Intel-Standard - two’s compliment of sum.
Example1: Data = 2002, checksum = lower byte of (0x100 – (0x20 + 0x02)) = 0xde
Example2: Data = 0000, checksum = lower byte of (0x100 – (0x00 + 0x00)) = 0x00
Example3: Data = fef0, checksum = lower byte of (0x100 – (0xfe + 0xf0)) = 0x12
End
Indicates the End of the frame
Size = 1 ascii character
Value = 125 Decimal (ascii } )
Ack/Nack
Positive acknowledge - Negative acknowledge
Size = 1 ascii character
Ack Value = 33 Decimal (ascii ! )
Nack Value = 63 Decimal (ascii ? )
Command Descriptions
Read Command Structure
The camera parses the sequence byte by byte. An invalid read command, target or index will cause the
camera to issue an NACK. The Host (You) will generate dummy data with a valid checksum then an end.
The camera will respond with an ACK and re send the command with valid data and checksum. If the
Host detects an error, it will re issue the command.
Host {r tt ii dummy dummy dummy dummy cc} camera issues !
Camera issues {r tt ii data data data data cc} (NOTE no ACK)
Write Command Structure
The camera parses the sequence byte by byte. An invalid write command, target, index or checksum
will cause the camera to issue a NACK, otherwise the write sequence will complete and the camera will
issue an ACK after the command has been executed. The camera receives the checksum from the Host.
Host {w tt ii data data data data cc} camera issues !
Error Checking
The camera parser is character by character and will respond with an immediate NACK if any
unrecognised command, target, index or checksum occurs.
Communication Timeouts
The camera micro controller uses a hardware watchdog timer that will time out if the time between
bytes are longer than 200ms. When sending command frames to the camera the host must not have
significant delays between bytes sent.
Normal <
50ms
Power up BIT
< 4s
Initiated BIT
< 2s
Power up
< 6s
Summary of Contents for MegaPlus ES 1020
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