From
This site:
This is the pinout for the serial port of the C64/C128. It is shown
facing the rear of the computer. Pinout is the same for CBM drives, but
then pins 3 and 6 are inputs. Serial cables are wired "straight through",
that is, pin 1 to pin 1, pin 2 to pin 2, etc.
5 1
6
4 2
3
PIN SIGNAL DIRECTION DESCRIPTION
1 /SRQ IN Enables fast serial, 128 mode only with 1571/81.
2 GND Logic ground.
3 ATN I/O Logic low = interrupt, then quiry for device #.
4 CLK I/O Clock - timing for slow serial data.
5 DATA I/O Data to/from computer/drive.
6 /RST OUT Logic low pulse from computer = reset periferals.
As you can see, the disk drive needs to be connected to the serial port of the Commodore 64
