80-Bus News


November–December 1983, Volume 2, Issue 6

Page 61 of 67


By Rory O’Farrell

My note on computer to computer communications in 80-BUS News Vol 2 No 5 has rapidly been outdated. I wrote then of the method of turning the file into HEX. Recently, I found an article in Microsystems (July 83) on the same subject, but much more elegant! Giving credit where it’s due, the author is Steven Fisher.

His method of getting the file into HEX is to use a Public Domain utility called UNLOAD. This utility takes a .COM file, and converts it into a file in .HEX format. He gives the entire object code for this in the form of a HEX listing. This is reprinted below. It can be typed up using a suitable editor, and saved to disc as UNLOAD.HEX. Then you use the command:


to convert it back to an object file. If you have any mistypings, these will show up as checksum errors, causing LOAD to protest and abort. Correct such errors by retyping or otherwise editing the lines in question, and go through the LOADing process again. When you have UNLOAD on your disc as a COM file, then you can try it out.

It is used by typing:


where FILE must have the extension .COM, which you need not specify, and 0100 is the address at which it is to live. This will create, on the same drive as UNLOAD, a new file called FILE.HEX. So far, so good!

Listing 2 is a short HEX listing of a file called PIPIO.HEX. This should be typed up in the same way as UNLOAD.HEX. Do not try to LOAD this. It contains the patch for PIP for communications.

With ZSID or DDT, patch as follows:

*** ***        ;ZSID answers with a size
£IPIPIO.HEX    ;Insert the name of the file to be used
£R0            ;Read it, Zero offset
£G0            ;Exit

A copy of PIP with this modification will need to be on both receiving and transmitting machines. The easiest way is to PIP the HEX files from one to the other, as the HEX files are ASCII, and short enough not to cause any problems with data loss through disc accesses.

To use this method of transfer, set up the PUN: to be a PTP: and the RDR: to be a PTR: on both machines. UNLOAD the file you require to transmit, then on the receiving machine type:


and on the transmitter:


During the course of the transfer, the computers will each respect the other’s need for disc accesses, and the cursor will be restored when the file is finally completely transmitted. Then you need only LOAD it on the receiving machine, and voila!

Page 61 of 67