This DDE transport protocol exchanges one or more files between the Host and PC in either direction in a single session. The exchange is controlled by the Host.
|PIC X(4)||VALUE “TAP ”|
|PIC X(42 max)||Optional. You may present the first parameter frame here (in which case skip to step 3).|
|PIC XX||Transfer Type:|
VALUE “XR” if sending a file to the PC and the PC should rename any previous version as .BAK,
VALUE “XA” if sending a file to the PC and the PC should first delete any previous version,
VALUE “XW” if requesting a file or file group from the PC.
|PIC X(40 max)||Filespec of file or file group on the PC (variable length string).|
Type XR is fail-safe because a .TMP workfile holds the new version until the transfer is complete. Type XA is not fail safe but maximises available space on the target media. A filespec comprises a filename optionally preceded by its MS-DOS directory “path”. A file group is defined by including “wildcard” characters * and or ? within the filename.or the Host sends an empty frame (go to step 5).
|PIC X||Frame Type: VALUE "H"|
|PIC X(12 max)||Filename (excluding the MS-DOS directory "path").|
|PIC X||Frame Type: VALUE "R"|
|PIC X(var)||Printable content.|
The PC sends a File Header for each file (if any) matching filespec in the Parameter frame. Each File Header is followed by the sequence of File Records (if any) within that file. The Host must send a Proceed condition code after every data frame from the PC. Within the PC source file, File Records are terminated by ASCII byte CR (0Dhex); all other non-printable bytes are discarded except HT (09hex) which is replaced by SP (20hex). When there are no more data frames the PC sends GS and goes to step 2.or the PC sends US if it did not receive the previous frame correctly (Host must repeat previous frame and return to step 3),
The PC adds the frame to the received file, appending the two ASCII bytes CR LF (0Dhex 0Ahex) and separating any fields within the frame with the single byte HT (09hex). Therefore, each data frame should contain a single record.or the Host sends a Condition Code (see below) (go to step 3).
|(this is an empty frame)|
Indicates that the Host has sent all the data frames for the current file.
|(this is an empty frame)|
Indicates that the Host is ready to receive the next Data Frame.
|PIC XX||VALUE "ZC"|
Indicates that the Host requests PC to close the current file immediately. If the PC accepts this request it sends the Header for the next file, or GS if there are no further files, at step 3.
|PIC XX||VALUE "ZD"|
Indicates that the Host requests PC to terminate DDE immediately. If the PC accepts this request it sends ESC at step 3.