What Is Actually Sent In A Message; Maximizing Message Integrity - Christie Entero RPMWU User Manual

C.2.3 What is Actually Sent in a Message
Although you will send and read messages as strings of ASCII characters, the actual message travels as a
sequence of bytes. Each character in this sequence requires 1 byte. The example below illustrates a "lamp limit
is 2000 hours" reply from the projector.
ASCII =
HEX =
C.2.4 Maximizing Message Integrity
For additional reassurance and/or maximum message integrity, you can insert one or two special characters:
• ACKNOWLEDGMENTS: If you want assurance from the projector (or group of projectors) that a set
message has been processed, request an acknowledgement. The acknowledgement is returned after the
message has been received and fully executed by the projector (i.e. in the case of a source switch it is not sent
until the switch is complete). If the message is not able to execute for some reason (i.e. invalid parameters,
timeout, etc) a NAK is returned instead (not-acknowledge). Note that requesting an acknowledgement serves
no purpose when included in a request message, since the acknowledgement will be redundant to the actual
reply from the projector. However, if requested, the "$" acknowledgement from the projector will follow the
reply.
There are two types of acknowledgements:
• SIMPLE ACKNOWLEDGEMENTS: Insert a "$" character just after the start code "(". This will only
return a '$'. This will only return a '$' on success, or a '^' on failure (NAK).
• FULL ACKNOWLEDGEMENTS: Insert a "#" character just after the start code "(". This will return
the message sent, as a reply.
This is a quick way to confirm success with set messages, and is particularly useful with long-distance
communication links or where the projectors and/or images are not visible from the controller.
Acknowledgements can also be a type of flow control.
• CHECKSUMS: For maximum message integrity, add a checksum character "&" just after the start code
"(". You must then also include the correct checksum total (0-255) just before the ")" end code. Make sure to
add a space before the calculated checksum to separate it from the last data parameter:
The checksum is the low byte of the sum of the ASCII values of all characters between the "("and the
beginning of the checksum, but not including either. It does include the space in front of the checksum.
Calculate the checksum for the above "set contrast to 64" command as follows:
CHECKSUM EXAMPLE = & + c + o + n + 6 + 4 + 'space'
= 26h+63h +6Fh +6E h +36h +$34h +$20h
= 01F0h
= F0h when only the low byte is used
= 240
The projector collects all of the message bytes as defined in the first byte of the message, then creates its own
checksum value for comparison with the checksum included in the controller's message. If the values match,
the message is considered to have been correctly received—otherwise the message is discarded.
'h' indicates a hex number.
NOTES: 1)
"acknowledge" and "checksum", either character can occur first.
Entero RPMWU/RPMSP/RPMHD-LED01 User Manual
020-100367-05 Rev. 1 (06-2012)
( L P
0x28 0x4 0x50
If a "request" message has a checksum so will the reply.
2)
L ! 2
0x28 0x21 0x32
Appendix C: Serial Command Overview
0 0 0
0x30 0x30 0x30
)
0x29
If using both
3)
C-5