Floppy disc controller

The Amstrad floppy disc interface is part of the design of the CPC664, CPC6128 and CPC6128+.

To use floppy discs with the CPC464 or CPC464+ a disc interface is required. There are two major floppy disc interfaces:

To use floppy discs with the CPC464+ there are two options:

Amstrad floppy disc interface

This interface uses a NEC 765A floppy disc controller (FDC) operating at 4Mhz, and has the following limitations:

The following restrictions apply to disc drives:

The disc operating system (AMSDOS) has the following restrictions:

The "polling" method is used to communicate with the FDC.

For each data transfer, the main status register (MSR) is read to determine:

All data transfers are through the data register of the FDC. (You are advised to read the official data-sheets covering the FDC for more information about the commands.)

The floppy disc drive interface is accessed using I/O commands (OUT, IN etc)

When bit 11 and bit 7 of the I/O address is set to "0" the FDC will be selected and bit 8 and bit 0 will select the operation as shown in the table below:

b8 b0 Function Read/Write state
0 0 FDD motor control Write Only
0 1 not used N/A
1 0 Main Status register of FDC (MSR) Read Only
1 1 Data register of FDC Read/Write

It is advised that the remaining bits of the I/O address are set to "1" to avoid conflict with other devices. The recommended I/O addressess are:

I/O address Function
&FA7EFDD motor control
&FB7EMain status register of FDC
&FB7FData register of FDC

FDD Motor Control

The FDD motor is controlled by OUTing values to this I/O port.

Bit 0 defines the state of the FDD motor:

The values of bit 7-1 are ignored.


Bit(s) Function
7..1 Ignored
0 FDD motor control: 1=active, 0=in-active

DDI-1 floppy disc interface

The DDI-1 package comprises:

FD-1 floppy disc drive

The FD-1 package comprises:

Vortex floppy disc interface

Details on this disc interface are welcome!

Using a disc drive with a Amstrad

To connect a 3.5" or 5.25" disc drive to the CPC664, CPC6128 or CPC6128+ as a second drive is easy:

To use the full capacity of a 3.5" or 5.25" floppy disc you will need another disk operating system (e.g. Parados), because AMSDOS only supports 40-track single sided discs.

Amstrad 3" floppy disc drives and disks


The Amstrad CPC664, CPC6128, CPC6128+ and DDI-1 disc interface use 3" discs.

The discs are rectangular in shape, have a stiff outer plastic covering and a metal shutter protecting the media inside. The disc can be inserted on either side so it is possible to use both sides with a single sided disc drive.

Disc drives

The disc drives are 40-track double-density single-sided.