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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.

ibm_xebec_step_pulses.bmp


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.