Project:
UUPX = Universal User Port Xfer system.

Purpose:
To be able to transfer data between any two Commodore 8-bit computers with user ports, from the PET to the C65.

Cable:
The cable is very simple.  You need two user-port connectors and an 11 (or 12) conductor cable.
Connect all the pins on the lower row of the user ports together on either end of the cable (A-N), *EXCEPT* you should
transpose pins B and M on one end of the table.  i.e.:


A  B  C  D  E  F  H  J  K  L  M  N
!  !  !  !  !  !  !  !  !  !  !  !
!  !  !  !  !  !  !  !  !  !  !  ! 
A  M  C  D  E  F  H  J  K  L  B  N

Pins A and N are ground.  You only need one of them connected, but connecting both is OK too.

Software:

uupx64.bin   ML = ($c000 / 49152)
uupxpet.bin  ML = ($1000 / 4096)
----
Control software with load, save, transmit, receive code.
ML = 49152 on C64, and 4096 on PET.

LOAD:
CALL: SYS ML
INPUTS:
   DEVICE CHANNEL 8 opened for read
   ML + 12 - low byte of buffer locations
   ML + 13 - high byte of buffer locations
OUTPUTS:
   ML + 14 - low byte of buffer end
   ML + 15 - high byte of buffer end
   * First two bytes of buffer are load address

SAVE:
CALL: SYS ML+3
INPUTS:
   DEVICE CHANNEL 8 opened for write
   ML + 12 - low byte of buffer start
   ML + 13 - high byte of buffer start
   ML + 14 - low byte of buffer end
   ML + 15 - high byte of buffer end
   * Values in ML + 12 and ML + 13 are also the first two bytes written
   
XFER OUT:
CALL: SYS ML+6
INPUTS:
   ML + 12 - low byte of buffer start
   ML + 13 - high byte of buffer start
   ML + 14 - low byte of buffer end
   ML + 15 - high byte of buffer end
   * First two bytes of buffer is receiver buffer address low/high
OUTPUTS:
   Routine will exit normally/rts when transfer is complete.   
   
XFER IN (RECEIVE)
CALL: SYS ML+9
INPUTS:
   NONE! Will receive data at address specified by transmitter.
OUTPUTS:
   ML + 12 - low byte of buffer start
   ML + 13 - high byte of buffer start
   ML + 14 - low byte of buffer end
   ML + 15 - high byte of buffer end
   * Routine will not exit until the STOP key is pressed.
     Wait until the transmitter exits, then hit STOP on the receiver.

Important locations:
1280 datadir = $e843
1290 datareg = $e841
1300 datairq = $e84d
1305 datairs = $e84e
1310 dataack = $e84c

C64
1280 datadir = $dd03
1290 datareg = $dd01
1300 datairq = $dd0d -   16?!    act=144, clear=127
1310 dataack = $dd00 - 56576 act=3, inact=7