Marquee 8521 Ultra Green (HUD) User's Manual
B-10
Marquee Projectors RS-232 Control
B.7 Creating
Simple
Messages
Figure B-4 below illustrates a complete RS-232 data transmission using the hex command codes
from Table B-4. In this example, the projector is “0” and the message is coming from the controller
(always 1023). Note that in this example contrast
level
is the only parameter involved.
X
0
1 2
3 4
5
6
7
X X
St
ar
t M
es
sa
ge
M
es
sa
ge
L
en
gt
h
D
es
tin
at
io
n
(2
b
yt
es
)
S
ou
rc
e
Fi
el
d
(2
b
yt
es
)
C
om
m
an
d
C
od
e
(1
b
yt
e)
P
ar
am
et
er
#
1
(1
b
yt
e)
P
ar
am
et
er
#
2
(1
b
yt
e)
C
he
ck
su
m
(o
pt
io
na
l)
E
nd
o
f M
es
sa
ge
(01)
HEADER
BODY
(00)(0E)
01 07 00 00 03 FF 56 40 00 0E
HEADER
BODY
Message length
is 7 bytes
To Proj. “0”
From controller
Set contrast
Contrast level
(P1)
=
transport layer byte
Figure B-4. The “set contrast to 64” command
The above data transmission is one of the sample messages in Table B-4. A comparison with code
in the other three “contrast” commands reveals how identically structured transmissions differ in
content and function. For example, note that the request message has no data (P1), thus it is only 6
bytes in length. In the resulting reply message from the projector, the controller (03 FF) is now the
destination and the projector (00 00) is the source, thus the codes for these two fields are likewise
reversed. The “D6” byte signifying request or reply is drawn from the list of codes in Table B-3.
Note that several of the sample messages in Table 5 include escape ($1B) codes to prevent
message bytes from being interpreted as transport layer bytes. For example, in the first four controls
shown (power, standby, picture mute and audio mute), the normal “on” code of $01 must be escaped
with the insertion of $1B and the addition of $80 to $01. Thus “$01” is replaced with “$1B $81”.
Commands that are more complex (standby, picture mute, projector address, signal status, ping, and
the test pattern diagnostic) are described in detail on the pages following Table 5.
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