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Clarity Visual Systems
September 1999
98
RS-232 Control
Transmission Speed 19200 BAUD
Transmission Data Data Length: 8, Stop Bit: 1, Parity Bit: None
No standard hardware or software pacing is used such as DTR/RTS or
XON/XOFF. Commands should be paced using the ACK, NAK, UNK, or ERR
responses from the display.
Standard RS-232 levels, +/- 12V, are used. Some laptop PC’s use ground
and +5V and are not always successful in communicating with the display.
The display’s RS-232 port is always active except during the boot process
which is the first 10 seconds after power is applied to the display electronics.
In single address mode (not when global commands are being used) the host
machine should wait for an ACK, NAK, UNK or ERR response from the
display before sending the next command to avoid overrunning the input
buffer. When global commands are sent, the displays will not return a
response, so a delay of ½ second should be maintained between commands
to avoid possible errors.
The protocol for communication to the display consists of a 7 byte command
line as described below.
STX(1 byte) IDT(2 byte) CMD(3 byte) ETX(1 byte)
Where;
ASCII STX - Start of transmission character, = 02h
Description Abbreviation Hex Decimal Character Control
Start of Text STX 02 2
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