Re: PC to RS485 bridge

["Neil Wrightson" <neilw@xxxxxxxxxx>]

Hi Frank,

Thanks for the feedback.

Something needs to turn the pseudo code of
{
COMMAND=CLEAR
TEXT=CURRENT LOUNGE TEMP \n23.12
DELAY=30
}
into something that a low level device can under stand.
Remebering that we are trying to keep the data transfer on the RS485
bus down and also allow for lower capacity devices to also play a part
on the 485 bus. So sending -
COMMAND=CLEAR
TEXT=CURRENT LOUNGE TEMP \n23.12
DELAY=30
on the bus seems a bit heavey and expecting pics etc to have a large
enough decode area is proably a bit much.

So if the PC wanted to send you above example to a OSD device it would
send the following command.
02   Stx
20   Address of OSD deviceBridge is address 0
??   Length of message
'C'  xpl-status  C=Remote command to be sent to a slave device
XXX  07H,'CURRENT LOUNGE TEMP',0DH,1EH,'23.12',0DH,0F
xx   Checksum
03    ETX

The xxx equeats to Clear screen,write text,CR,delay for this line, text
on next line,CR,delay for this line.
In the On Screen Devices I have developed, I actually use ClearScrean &
GotoXY commands. This allows the PC to do the screen or line clearing
or clearing of three characters at a certain XY location


Neil.




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