IBM Fixed Disk Adapter - Head Stepping Pulses
The 'IBM Fixed Disk Adapter' is the hard drive controller that Xebec made for IBM's use in the IBM 5160 (IBM XT).
I sometimes refer to these as the 'IBM/Xebec HDD controller'.
The following image shows an example of head step pulses (negative-going) being sent by the IBM Fixed Disk Adapter to whatever hard drive is attached.
In the example, a group of 5 pulses is being sent.
As can be seen, the IBM Fixed Disk Adapter generates step pulses of:
* Step pulse width of 17 µs
* Step pulse rate of 70 µs
Not all hard drives have step timing requirements that are compatible with the above. The Seagate ST-506 is an example. Such drives will not step properly.