The X-MASS is an ATA/IDE interface for the CPC made by ToTO.
The device uses the same IDE I/O ports (except for the alternative status register and drive address register) than the Symbiface 2 and is therefore compatible with it.
The port range it supports is FD08-FD0F.
The device also has a Disk-On-Module IDE device connected. This is connected as master and by default the X-MASS only supports a single device.
It should be possible to remove this and use other compatible ATA devices with an adaptor provided they support 8-bit data transfer.
When the X-MASS is powered on the CPC is held in reset while the X-MASS communicates with the Disk-On-Module. If all is good the reset is released and the CPC starts up.
During this reset time the X-MASS sets the device into 8-bit PIO mode using SET FEATURES ATA command. The X-MASS device therefore requires "newer" IDE devices which support the CFA ATA mode because the 8-bit PIO is part of that command set.
It is possible to use SET FEATURES to put the X-MASS into 16-bit mode, but then you would only read 8 of the 16-bits of data that ATA devices often use, and you would only be able to use half the capacity of the device and you would not be able to read devices formatted on the PC for example.
In default configuration the X-MASS operates the same as the Symbiface 2 IDE and has the same functionality.
The I/O ports operate in a "pass-through" like mode where the registers directly reflect those of the connected ATA device.
Like the Symbiface 2, the device should be selected with port FD0E first, then the other I/O ports can be used to program the selected device.
The I/O port is decoded fully:
1111 1101 0000 1xxx (xxx for registers 8-f)