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Contents
33FD/53FD DISKETTE DRIVE AND ERROR CONDITIONS 8-50
ATTACHMENT (Level 1) 8-1 Fast Check . . . . . 8-52
INTRODUCTION 8-1 Not Ready . . . . . 8-52
Diskette Addressing . . 8-1 Missing Erase Current and Unexpected or
33FD Diskette Drive . . . 8-2 Erase Current Present . . . . 8-53
33FD Diskette Drive Assembly 8-2 ID Not Found (Missing Record) 8-53
33FD Operating Sequences 8-3 Read Overrun Check . 8-54
Frequency Modulation Read and Write Circuits 8-4 Write Overrun Check . 5-54
Diskette 1 Format. . . . . . 8-5 Write Parity Check. . 8-54
53FD Diskette Drive . . . . . . 8-6
53FD Diskette Drive Assembly 8-6.
53FD Operating Sequences 8~ 7
Modified Frequency Modulation Read and
Write Circuits ... 8-8
Diskette 20 Format 8-9
DATA FLOW . . 8-11
OPERATIONS. . 8-12
Seek Operations . 8-12
Seek Data Flow 8-13
Read Operation 8-14
Read Data Flow 8-17
Write Operation 8-18
Write Data Flow . 8-19
Find Sector Identification Operation 8-20
Find Sector Identification Data Flow 8-23
Write Sector Identification Operation. 8-24
Write Sector Identification Data Flow 8-25
COMMANDS . . . . .. 8-26
I/O Load Command . . . . 8-26
I/O Sense Command 8-28
I/O Control load Command 8-30
Write Byte or Write Address Mark Byte
Command . . . . . . . . . . . . . 8-32
Write Data Trigger . . . . . . . . 8-34
Write Cyclic Redundancy Character Byte
Command . . . . . . . . . . . . . 8-35
Seek to Next Track Command 8-37
Search for Address Mark Byte Command. 8-38
I/O Control Sense Command . . . . . . 8-40
Sense Interrupt Level Status Byte Command 8-43
Jump on I/O Command 8-44
FUNCTIONAL UNITS 8-46
Data Separator 8-46
I ndex Counter . . . . 8-46
Ready Counter 8-47
Control Storage Initial Program Load Track
Counter . . . . . . . . . . 8-47
Write Clock and Write Bit Ring . . . . . 8-47
Read Clock and Read Bit Ring . . . . . 8-47
Cyclic Redundancy Character Shift Register . 8-48
Interrupt 1 and Interrupt 4 Requests . . . . 8-49




Contents for 33FD/53FD Diskette Drive and Attachment (Level 1)
33FD/53FD Diskette Drive and Attachment (Level 1)
Diskette Addressing
INTRODUCTION

Sequential Sector Addressing
The diskette drive and diskette drive attachment
are installed inside the 5340 System Unit. The main storage program uses sequential
System/34 uses either a 33FD diskette drive or sector addressing to identify a diskette data
a 53FD diskette drive. The control storage area. Sequential sector addressing starts at
program and the attachment control the hexadecimal address 0001 (cylinder 1, data
diskette drive. The diskette drive can read a head 0, sector 1), increases by 1 for each
data track, write on a data track, or seek to a following sector, and extends through the last
data track of a diskette. sector on cylinder 74. Cylinder a cannot be

The diskette drive has a continuously turning
shaft that turns the diskette. A solenoid-loaded
data head is moved to the correct data track by
00 addressed by sequential sector addressing.

The control storage program changes sequential
sector addresses to actual sector addresses for



D
a stepper motor. The data head can then read all operations. See the Data Areas Handbook for
or write the data tracks. more information on diskette addressing.

One side of the Diskette 1 (33FD /53FD




-----00
diskette) and both sides of the Diskette 2D Actual Sector Addressing
(53FD diskette) are used for recording. The
two types of diskettes are identified by the If sequential sector addressing is not used,
physical location of the index holee. When a Diskette Drive actual sector addressing is used. The user
Diskette 1 is inserted in a 53FD diskette drive, supplies the 5-byte CHRNX field. This method
the circuits that sense the index hole prevent Card Side of addressing must be used to address cylinder
the use of the second side. A Diskette 2D a (the volume label and volume table of
cannot be used in a 33FD diskette drive. contents).

There is one label cylinder, 74 data cylinders,
and two alternative data cylinders per diskette.
Diskette Drive Attachment Diskette Drive
For more information, see The IBM Diskette
Diskette
General Information Manual, GA21-9182.
I I I
D I., ;4-
Index Hole for Index Hole for
I
Instructions executed by the control processor
I Write Circuits
I
I ~~~~s~:e! diskette)_ I Diskette 2D
(two-sided diskette)

. r--------.