1. Serial communications Basics
Some commands do not require a data field(s)
Checksum byte
The “Checksum byte” is used to detect errors during transmission or reception
Checksum byte = (projectora command bytes + Data bytes) Modulo \x100
Stop byte
The “Stop byte” informs the projector (in case of transmission) or the computer (in case of reception) that the data transfer is complete
and that the interpretation of the command and data bytes can start.
Acknowledge (ACK)
If the communication link and if the sent commands can be interpreted by the projector an “
ACK
” command is sent back. In case the
commands cannot be interpreted a “
NACK
” command is sent back.
End of process (EOP)
When the end of process command is activated, an EOP is send after the ACK command to signify the completion of the process.
for more information about this, see the EOP command.
Note
Any command byte, data byte or checksum byte that equals
\x80, \xfe, \xff
has to be converted !
1.
Transmission
- instead of
\x80
, send
\x80
followed by
\x00
- instead of
\xfe
, send
\x80
followed by
\x7e
- instead of
\xff
, send
\x80
followed by
\x7f
2.
Reception
- replace
\x80
followed by
\x00
with
\x80
- replace
\x80
followed by
\x7e
with
\xfe
- replace
\x80
followed by
\x7f
with
\xff
1.2
Data words
msb
The
m
ost
s
ignificant
b
yte, is the byte with the greatest weight (value).
lsb
The
l
ess
s
ignificant
b
yte, is the byte with the smallest weight (value).
Description
A word contains more than one byte, the first byte is the msb, the last byte is the lsb.
Examples of data words
•
The projector runtime parameter is described using an unsigned double word where 2 bytes (msb ...lsb) represent the value of
the runtime in seconds.
How to calculate the value of a word ?
Lets take the example of a double word returned by the “
projector runtime, read
” commando.
6
R5976884 RLM SERIES 04/04/2006
