
                  IEEE488 to CBM serial IEC bus converter
                                      
                               (c) A. Fachat
                                      
   Way back I together with a friend developed an IEEE488 to CBM serial
   IEC bus converter for his CBM610, to use the VC1541.
   
   When I mentioned this interface on the net, I was asked to release it,
   and here it is. However, I have digged this interface up from a long
   stored archive (which I salvaged from an Atari ST SCSI harddisk after
   my Atari gave up by patching the parition table by hand etc...) So I
   don't know if this is final version, and the schematic is lost as
   well. I reengineered it and included a description in the xa65 source
   file.
   
   The serial IEC bus interface is similar to that of the C64.
   
   The IEEE488 interface uses the standard 75160 and 75161 IEEE interface
   drivers and an unusual chip, the 6532 RIOT (RAM-I/O-Timer). Well, I
   doubt if one can get this chip today actually, but I think it could
   easily be replaced with normal static RAM and two VIA or CIA. The
   timer handling might be confusing, but you had to write a value twice
   to ensure that the timer starts. This should be easier with the VIA.
   
   Some information on the RIOT 6532 can be found on funet.
   
  Disclaimer
  
   There is absolutely NO WARRANTY, neither expressed nor implied! Noone
   can be held responsible for any damage arising from the use or
   building of this interface or even from reading these pages! I do not
   claim nor guarantee that the hardware and software can be used for
   anything useful! 
   
  Files
  
   The par2ser.a65 xa65 source file with hardware description. After the
   first version we found out that the PET (i.e. CBM610 in a friends
   case) doesn't send a secondary address to the printer, causing the
   first version to send everything to the serial bus with ATN (lacking
   the secondary address to reset serial ATN). I don't know if this is
   already the fixed version.
   
   The ROM, that is made from this file is in par2ser.rom. It includes a
   two-byte loading address at the start of the file.
   
   From this version I reverse-engineered the schematics of this little
   computer. You can find it in par2ser.ps or par2ser.png. The xfig
   source for those schematics is in par2ser.fig.
