Washington Apple Pi

A Community of Apple iPad, iPhone and Mac Users

1 2 3 4 5 6 7 8 9 10 11 12 13 14

5.0 Data File Transfer

Data communications parameters are a little more critical during file transfer than during normal chatting. You must have the same settings on the communication programs on both ends of the line.

Obviously, if you are using 9600 baud on one end, then you should NOT have the other end set up for 1200. In addition, you should check to see whether "line feeds" follow each carriage return and whether your communications program is set up to "filter" out certain characters.

Another thing to consider is that there are different ways of transferring data. These methods are called "transfer protocols" and the main ones I use are ASCII and XMODEM. The Ascii protocol is the "Vanilla" of this kind of communications. It is sometimes referred to as "No protocol". CompuServe calls it DC2/DC4 Capture protocol. XModem is more like the double chocolate flavor and is described in more detail later. You will need to have the same method available on both sides of the process.

The simplest way to transfer data is with ASCII transfer. This works fine with text files. Ah, but what is a "text" file?

A simplistic definition of a text file is that it can be edited with the Pascal editor and contains only printable characters. I am not going to attempt a thorough explanation of the difference between "Text" and "binary" files, but you may need to understand this area before going too far with RS232 communications. The underlying problem is that some bytes (each character uses one byte) are used for commands in ASCII protocol and therefore (a) cannot be successfully transferred and (b) will probably interrupt the transfer.

The Apple /// operating system (SOS) assigns a "file-type" to each file. The ones I have seen are "Asciifile", "Textfile", "Codefile", "Datafile" and "Sosfile". This "file-type" can be independent of the file name suffix. The preferred convention is to use a suffix that identifies the file-type and this is usually done. Files with the suffix ".code" usually have a file-type of "Codefile" and other suffixes are used similarly. However, it is possible to assign any suffix to any file and not knowing this can lead to a great deal of confusion. Just changing the suffix of a file does not change its file-type.

The word "text" has three separate uses in relation to the Apple /// files.

(1) The first use is in contrast "text" files with "binary" files, as discussed above. "Text" files can be transferred with ASCII protocol, binary files require a different protocol. In general "text"files can be edited and read as text while binary files are usually read only by computer programs. Files with file-types "Asciifile" and "Textfile" are text files. Files with other filetypes are binary files.

Return to Apple III Home Page

Revised November 1, 1998 lic
Washington Apple Pi
URL: http://www.wap.org/a3/