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Hardware (Logic) Control of Headswitch for a Hard Magnetic Disk File With Enhanced Small Device INTERFACE

IP.com Disclosure Number: IPCOM000034158D
Original Publication Date: 1989-Jan-01
Included in the Prior Art Database: 2005-Jan-26
Document File: 7 page(s) / 187K

Publishing Venue

IBM

Related People

Anderson, CA: AUTHOR [+3]

Abstract

This hardware state machine gives faster response to the Enhanced Small Device Interface (ESDI) controller when a head switch occurs, and it changes heads on the file at a precisely controlled point. (Image Omitted) The hardware (logic) controls head switches for a hard file using sector servo imbedded on the data surfaces with the ESDI. Since the host performs head switches when using the ESDI, a file with sector servo must control the head switch time so that servo read is not disturbed. In addition, the servo microprocessor is notified of head switches to perform a "settle" when it occurs. Command Complete is controlled by the logic to allow head switches during seeks and other ESDI operations. The Head Select logic has the following objectives: 1.

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Hardware (Logic) Control of Headswitch for a Hard Magnetic Disk File With Enhanced Small Device INTERFACE

This hardware state machine gives faster response to the

Enhanced Small Device Interface (ESDI) controller when a head switch occurs, and it changes heads on the file at a precisely controlled point.

(Image Omitted)

The hardware (logic) controls head switches for a hard file using sector servo imbedded on the data surfaces with the ESDI. Since the host performs head switches when using the ESDI, a file with sector servo must control the head switch time so that servo read is not disturbed. In addition, the servo microprocessor is notified of head switches to perform a "settle" when it occurs. Command Complete is controlled by the logic to allow head switches during seeks and other ESDI operations. The Head Select logic has the following objectives: 1. Detect when the controller wants to change the

present data head.

2. Change the old selected head to the new selected

data head.

3. Check for valid data head selection.

4. Control ESDI COMMAND COMPLETE interface line.

5. Tell the interface microprocessor and the servo

microprocessor of the new head selection.

6. Detect multiple head selections before first head

selection has settled.

7. Remember the last valid head selected.

8. Do not switch heads when the data heads are over a

sector servo area. For this function the ESDI has four lines on the interface. These are:

(Image Omitted)

HEAD SELECT 2(0)

HEAD SELECT 2(1)

HEAD SELECT 2(2)

HEAD SELECT 2(3) These four lines allow selection of each individual read/write head in a binary coded sequence. HEAD SELECT 2(0) is the least significant line. Heads are numbered 0 through 14, (number 15 is not supported). When all HEAD SELECT lines are high (inactive), head 0 will be selected. Addressing more heads than contained in the drive will result in a write fault when attempting to perform a write operation. Addressing more heads than contained in the drive will result in no data being transferred on the interface when attempting to do a read operation. The four lines will be terminated on the board with a 150-ohm resistor, and the receiver will be a Schmitt trigger inverter. The Head Select Logic will detect the change in these interface lines and, if the drive is selected,

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will tell the interface microprocessor, via a polled interrupt, that a head switch occurred and will also latch up this new head selection. The Head Select Logic will deactivate the COMMAND COMPLETE interface line upon detecting a head

(Image Omitted)

switch. The interface microprocessor will also tell the servo microprocessor about the head change. The servo microprocessor will inform the interface microprocessor when the head has settled down. Following this, the interface microprocessor will then tell the Head Select Logic that the COMMAND COMPLETE interface line can be reactivated. The Head Select Logic will compare the interface lines to the latched hea...