# Side Switch

AMSDOS is designed for single sided disc drives, and the disc drive in the CPC664, CPC6128, CPC6128+, DDI-1 and FD-1 are single sided. However, it is possible to use both sides of a 3" floppy disc by turning it over.

But, if you have a 3.5" second drive you will only be able to use one side of a 3.5" floppy disc because it is not possible to turn over a 3.5" disc and put it into the drive!

If you want to use both sides with AMSDOS, you will need a side switch.

The side switch is designed so that you can use:

- both sides of a 3.5" disc with the AMSDOS disk operating system,
- software written for 3" discs on a 3.5" disc (e.g. games)

Note, that the CPC floppy disc controller does support double sided disc drives, and both sides can be used if you use another DOS. (e.g. C/PM, Parados, Romdos etc).

The switch has two positions.

Position 1:

When the switch is in position 1:

- side 1 can be used with AMSDOS
- both sides can be used with another DOS.

When the switch is in position 2:

- side 2 can be used with AMSDOS
- do not use this position with another DOS, because only side 2 will be selected!

#### The switch

The switch is a SPST (Single-Pole, Single-Throw) toggle type. The switch is locking in both directions, and has 3 contacts.

The switch:

The connections:

This switch can be fitted internally or externally.

                Cable

    SIDE 1 SEL |     | GND
               |     |
               o     o
                \
    SPST switch  \
                  o
                  |
                  |
                  | Side 1 Sel

                 FDD

#### Technical

The side select signal is generated by the FDC and is active low.

- When side 1 is selected "/SIDE SELECT" signal to the disc drive will be "1"
- When side 2 is selected "/SIDE SELECT" signal to the disc drive will be "0".

When the switch is in position 1, the side select signal is not changed:

- "/SIDE SELECT" input to the switch will become "/SIDE SELECT" output from the switch,

Therefore the drive will access either side 0 or side 1, depending on the "/SIDE SELECT" output from the FDC. When used with AMSDOS, side 1 will always be accessed. When used with another DOS that supports double-sided discs, side 1 or side 2 can be used.

When the switch is in position 2, the signal is forced to "0":

- "/SIDE SELECT" output from the switch will be "0"

Therefore the drive will always access side 2.