Product Review: Pro-Lite Scrolling Message Signs
Only a minimal understanding is needed in order to operate the sign. Mastery requires becoming familiar with the protocol and doing a little experimenting.
Multiple signs can be connected to a computer over the same serial port by using a simple telephone-line-splitting Y-connector. Each sign has an assignable logical address that allows you to send messages to particular signs. A logical address is represented in hexadecimal as a number between 01 and FF. Addresses may be shared enabling grouping; in this way, a message to ID01 goes to all signs with ID01.
Communication with the sign is always done with readable ASCII characters; thus, an arbitrary ID of 2F would be designated with the digit “2” and the capital letter “F”.
ID00 is reserved to mean “broadcast to all signs”. By default, a sign is preconfigured as ID01; this can be changed with the remote control. If you are addressing a single sign connected straight to the computer, it will respond with its ID number after each successful command. Messages sent to ID00 do not return a response, and neither does an individual sign when the line is shared via the Y-connector.
All messages to the sign, except for those setting the date and time, are sent in the following format followed by the carriage return/line feed: <IDxx>command, xx is 00 to FF. Any command longer than 1,023 bytes will be ignored by the sign.
To set the date and time, no ID is needed. The format is <TYYMMDDwhhmmss> where YY is the year, MM the month, DD the day, w the weekday (0=Sun, 1=Mon,...6=Sat), hh the hour, mm the minute and ss the seconds. This can be accomplished with the shell very easily. Set the date/time of all signs with the command:
ate "+<T%y%m%d%w%H%M%S>" te "+<T%y%m%d%w%H%M%S>" > /dev/prolite> /dev/prolite
The leading + sign tells the date command to build a string via substitution; see your man pages for details.
To signal a sign to start listening to responses, send it an empty command with the format <IDxx>; e.g., type:
echo "<ID01>" > /dev/prolite
The most fundamental concept of the sign is the idea of a page. A page consists of a message the sign is to display either now or some time in the future. Pages may contain text, numerics, symbols, font attribute tags, color tags, graphic tags and effect tags. There are 26 pages named, appropriately enough, A to Z. Case does matter when identifying a page.
Any given page can hold approximately 1,012 bytes of information. I say approximately because special tags (see sidebar) consume more than one byte, which means less space. Also, using some trickery by omitting the page directive completely and defaulting to page A squeezes out an additional two bytes, which means more space.
The command to set a page is <Px>, where x is the page name. Any text after this sequence is considered text for the sign. To set the message “Linux Rules” on page A, type the following command:
echo "<ID01><PA>Linux Rules" > /dev/prolite
It is important to leave extra space at the end so the end of the message is separated from the front of the message as it scrolls.
To delete a page, use <DPx>, where x is the page name. For example, to delete page B, type:
echo "<ID01><DPB>" > /dev/prolite
The sign is constantly displaying a page. If the default page A is scrolling by, then when its content is changed it will immediately start displaying the new message. Otherwise, we must tell the sign which page to run using the <RPx> command, where x is the page to display. Normally, the sign can run only one page at a time.
Once a page has been defined, it can be run. For example, to repeatedly display our message, type:
echo "<ID01><RPA>" > /dev/prolite
Running an undefined page will result in displaying the sign's demo.
Two points of interest for script writers:
It is possible to update the contents of a page not being displayed, then switch to that page at a later time.
It is possible to update the currently displayed message. The only problem is the display will be interrupted mid-message.
Sadly, you cannot ask the sign what the contents of a page are, what page it is currently displaying, or when it has started or ended a display sequence. Thus, techniques like double-buffering don't work for continuous messages.
I have received one terse message from Pro-Lite that alluded to a future version of the sign which is designed to address such needs explicitly for computer users.
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