IBM 5-1/4" Diskette Drive Adapter Application guide

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Personal Computer
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Hardware Reference
--_.-
Library
mM 5-1/4" Diskette
Drive Adapter
6361505

ii

Contents
Description .................................... 1
Programming Considerations
...................... 3
Digital-Output Register
...................... 3
Floppy Disk Controller
....................... 4
Command Summary
......................... 8
Programming Summary
...................... 17
Interface ..................................... 19
System
I/O Channel Interface ................ 19
Drive A and B Interface
..................... 20
Specifications
................................. 23
Logic Diagrams
................................ 25
Hi

iv

Description
The IBM 5-1/4" Diskette Drive Adapter fits into one of the
expansion slots in the system unit.
It is connected to one or two
diskette drives through an internal, daisy-chained flat cable. The
adapter has a connector
at the other end that extends through the
rear panel of the system unit. This connector has signals for two
additional external diskette drives; thus, the
5-1/4 inch diskette
drive adapter can attach four
5-1/4 inch drives -two internal
and two external.
The adapter
is designed for double-density, MFM-coded, diskette
drives and uses write precompensation with an analog phase-lock
loop for clock and
data recovery. The adapter is a
general-purpose device using the
NEe fLPD765 or equivalent
controller. Therefore, the diskette drive parameters are
programmable. In addition, the attachment supports the diskette
drive's write-protect feature. The adapter
is buffered on the I/O
bus and uses the system board's direct memory access (DMA) for
record data transfers.
An interrupt level also is used to indicate
when an operation
is complete and that a status condition requires
microprocessor attention.
In general, the
5-1/4 inch diskette drive adapter presents a
high-level command interface to software
I/O drivers.
Diskette Adapter 1

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Direction
Disk
8
Controller
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5-1/4Inch Diskette Drive Adapter Block Diagram
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Programming Considerations
This attachment consists of an 8-bit digital output register in
parallel with a
NEC JLPD765 or equivalent floppy disk controller
~ (FDC).
In the following description, drive numbers 0, 1, 2, and 3 are
equivalent to drives A, B, C, and D.
Digital-Output Register OJ / ..
The Digital-Output register (DOR) is an output-only register used
to control drive motors, drive selection, and feature enable. All
bits are cleared
by the II 0 interface 'reset' line. The bits have the
following functions:
Bits 0 and 1 These bits are decoded
by the hardware to
select one drive if its motor
is on:
Bit 1 0 Drive
00
o (A)
01
1 (B)
10
2 (C)
1 1 3
(D)
Bit 2 The
FDC is held reset when this bit is clear.
It must be set by the program to enable the
FDC.
Bit 3 This bit allows the
FDC interrupt and DMA
requests to be gated onto the I/O interface.
If this bit is cleared, the interrupt and DMA
request I/O interface drivers are disabled.
Bits
4,5,6,
These bits control, respectively, the motors of
and 7 drives 0,
1,2 (A, B, C), and 3 (D). If a bit is
clear, the associated motor is off, and the
drive cannot be selected.
Diskette Adapter 3

Floppy Disk Controller
The floppy disk controller (FDC) contains two registers that may
be accessed
by the system unit's microprocessor: a status register
and a data register. The 8-bit main status register contains the
status information
of the FDC and may be accessed at any time.
The 8-bit data register (actually consisting of several registers in a
stack with only one register presented
to the data bus at a time)
stores data, commands, parameters,
and provides floppy disk
drive
(FDD) status information. Data bytes are read from or
written to the data register in order to program or obtain results
after a particular command. The main status register can only be
read and is used to facilitate the transfer of data between the
system unit's microprocessor
and FDC.
The bits in the main status register (hex 34F) are defined as
follows:
Bit
Number
Name Symbol
Description
DBO
FDD A Busy
DAB FDD number 0 is in the Seek mode.
DB1
FDD B Busy DBB FDD
number 1 is in the Seek mode.
DB2 FDD C Busy DCB FDD
number 2 is in the Seek mode.
DB3 FDD D Busy DDB FDD
number 3 is in the Seek mode.
DB4 FDC Busy CB A read or
write command is in process.
DB5 Non-DMA
NDM
The FDC is in the non-DMA mode.
Mode
DB6 Data Inputl
DIO
Indicates direction of data transfer
Output
between FDC and processor. If DIO = "1;'
then transfer is from FDC data register to
the processor. If DIO = "0;' then transfer
is from the processor to FDC data register.
DB7 Request
for
ROM Indicates data register is ready to send or
Master
receive data to or from the processor. Both
bits DIO and ROM should be used to
perform the handshaking functions of
"ready" and "direction" to the processor.
The FOe is capable of performing 15 different commands. Each
command is initiated by a multi-byte transfer from the system
unit's microprocessor,
and the result after execution of the
command may also be a multi-byte transfer back to the system
4 Diskette Adapter

unit's microprocessor. Because of this multi-byte interchange of
information between the
FDC and the system unit's
microprocessor, it
is convenient to consider each command as
consisting of three phases:
,~ Command Phase
The FDC receives all information required to perform a particular
operation from the system unit's microprocessor,
Execution Phase
The FDC performs the operation it was instructed to do.
Result Phase
After completion of the operation, status and other housekeeping
information are made available to the system unit's
microprocessor,
The following tables define the symbols used in the command
summary. The command summary immediately follows these
tables,
Diskette Adapter 5

Symbol
Name
AO
Address Line 0
C
Cylinder Number
D Data
D7-DO Data Bus
DTL Data Length
EDT End
of Track
GPL Gap
Length
H Head
Address
HD Head
HLT Head Load
Time
HUT
Head Unload Time
MF FM or MFM Mode
MT
Multi-Track
N Number
Description
AO
controls selection of main status
register (AO = 0) or data register (AO =1 ).
C stands for the current/selected cylinder
(track) number of the medium.
D
stands for the data pattern that is going
to be written into a sector.
8-bit data bus, where D7 stands for a
most significant bit, and DO stands for a
least significant bit.
When N is defined as 00, DTL stands for
the data length that users are going to
read from or write to the sector.
EDT stands for the final sector number on
a cylinder.
GPL
stands for the length of gap 3
(spacing
between sectors excluding VCO
sync field).
H
stands for head number 0 or 1, as
specified in
ID field.
HD
stands for a selected head number 0
or 1. (H =HD in all command words).
HLT stands for the head load time in the
FDD (4 to 512 ms in 4·ms increments).
HUT stands for the head unload time after
a read or write operation has occurred (0
to 480 ms in 32-ms increments).
If MF is low, FM mode is selected; ifit is
high,
MFM mode is selected only if MFM
is implemented.
If MT is high, a multi-track operation is to
be performed. (A cylinder under both HDO
and HD1
will be read or written.)
N stands for the number of data bytes
written in a sector.
Symbol Descriptions (Part 1 of 2)
6 Diskette Adapter

-Symbol Name
NCN New Cylinder
Number
ND
Non-DMA Mode
PCN Present Cylinder
Number
R Record
R/W Read/Write
SC Sector
SK Skip
SRT
Step Rate Time
STO Status 0
ST 1
Status 1
ST 2
Status 2
ST 3 Status 3
STP Scan
Test
usa,
Unit Select
US1
Description
NCN stands for a new cylinder number
which is going to be reached as a result
of the seek operation. (Desired position of
the head.)
ND
stands for operation in the non-DMA
mode.
PCN stands for cylinder number at the
completion of sense-interrupt-status
command indicating the position of the
head at present time.
R
stands for the sector number, which
will be read or written.
R/W stands for either read (R) or write
(W) signal.
SC
indicates the number of sectors per
cylinder.
SK
stands for skip deleted-data address
mark.
SRT stands for the stepping rate for the
FDD (2 to 32 ms in 2-ms increments).
STO-3
stand for one of four registers that
store the status information after a
command has been executed. This
information is available during the result
phase after command execution. These
registers should not be confused with the
main status register (selected by AO = 0).
ST 0-3 may be read only after a command
has been executed and contain
information relevant to that particular
command.
During a scan operation, if STP = 1, the
data in contiguous sectors is compared
byte-by-byte with data sent from the
processor (or DMAL and if STP= 2, then
alternate sectors are read and compared.
US stands for a selected drive number
encoded the same as bits 0 and 1 of the
digital output register (DOR).
Symbol Descriptions (Part 2 of 2)
Diskette Adapter 7

Command Summary
In the following table, 0 indicates "logical 0" for that bit, 1 means
"logical
1," and X means "don't care."
Data Bus
Phase
R/W D7
D6 D5 D4
D3 D2 D1 DO
Read Data
Command
W MT
MF
SK 0 0 1 1 0
W X X X X X HD US1USO
W C
W H
W R
W N
W EOT
W GPL
W DTL
Execution
Result R ST 0
R ST 1
R ST 2
R C
R H
R R
R N
Read Deleted Data
Command
W MT MF
SK 0 1 1 0 0
W X X X X X HD US1USO
W C
W H
W R
W N
W
EOT
W GPL
W DTL
Execution
Result R
STO
R ST 1
R ST 2
R C
R H
R R
R N
Remarks
Command Codes
Sector ID information
prior
to command
execution.
Data transfer
between the FDD
and
main system.
Status information
after command
execution.
Sector ID information
after command
execution.
Command Codes
Sector ID information
prior to command
execution.
Data transfer
between the FDD
and
main system.
Status information
after command
execution.
Sector ID information
after command
execution.
8 Diskette Adapter

Data Bus
Phase
R/W 07 06 05
04
03 02 01 DO
Remarks
Write Data
Command W MT
MF 0 0 0 1 0 1
Command Codes
W X X X X X HD US1
usa
W C
Sector ID information
W H prior
to command
W R
execution.
W N
W EOT
W GPL
W DTL
Execution Data
transfer
between the main
system and FDD.
Result R
STO
Status information
R ST 1
after command
R ST 2
execution.
R C
Sector ID information
R H
after command
R R execution.
R N
Write Deleted Data
Command W MT
MF 0 0 1 0 0 1
Command Codes
W X X X X X HD US1
usa
w C Sector ID information
W H prior to command
W R
execution.
W N
W EOT
W GPL
W DTL
Execution Data
transfer
between the FDD and
main system.
Result R
STO
Status ID information
R ST 1 after command
R ST 2
execution.
R C Sector ID information
R H after command
R R execution.
R N
Diskette Adapter 9

Oata Bus
Phase
R/W 07 06 05 04
03 02 01 00 Remarks
Read a Track
Command
W 0 MF SK 0 0 0 1 0
Command Codes
W X X X X X HD US1 usa
w C Sector ID information
W H prior
to command
W R
execution,
W N
W EOT
W GPL
W DTL
Execution Data
transfer
between the FDD
and main
system,
FDC reads all of
cylinder's contents
from index hole to
EOT,
Result R
STO Status information
R ST 1
after command
R ST 2 execution,
R C
Sector ID information
R H
after command
R R execution,
R N
Read 10
Command
W 0
MF 0 0 1 0 1 0 Command Codes
W X X X X X HD US1 usa
Execution The
first correct ID
information on the
cylinder is stored in
data register,
Result R
STO
Status information
R ST 1 after command
R ST 2
execution,
R C Sector ID information
R H during execution
R R phase,
R N
10 Diskette Adapter

Oata Bus
Phase R/W 07 06
05 04 03 02
01 00 Remarks
Format a Track
Command W 0
MF
0 0 1 1 0 0 Command Codes
W X X X X X HD US1 usa
w N Bytes/Sector
W
SC
Sector/Track
W GPL Gap 3
W D filler
byte.
Execution FDC formats an
entire cylinder.
Result R
STO
Status information
R ST 1
after command
R ST 2 execution.
R C In this case, the 10
R H information has no
R R meaning.
R N
Scan Equal
Command W MT
MF SK 1 0 0 0 1 Command Codes
W X X X X X HD US1
usa
w C
Sector 10 information
W H prior to command
W R execution.
W N
W EOT
W GPL
W STP
Execution Data compared
between the FDD
and
the main system.
Result R
STO
Status information
R ST 1 after Command
R ST 2 execution.
R C
Sector ID information
R H after command
R R
execution.
R N
Diskette Adapter 11

Data Bus
Phase R/W
07
06 05 04
03 02
01 DO
Remarks
Scan
Low or Equal
, , ,
Command
W MT
MF SK 0 0
Command Codes
W X X X X X
HD US, usa
W C
Sector ID information
W H prior
to command
W R
execution.
W N
W EOT
W GPL
W STP
Execution Data compared
between the FDD
and main
system.
Result R
STO
Status information
R
ST'
after command
R ST 2
execution.
R C
Sector ID information
R H
after command
R R
execution.
R N
Command
W MT
Scan High or Equal
MF SK , , , 0 ,
Command Codes
W X X X X X
HD US, usa
w C
Sector ID information
W H prior
to command
W R
execution.
W N
W EOT
W GPL
W STP
Execution Data
compared
between the FDD
and main
system.
Result R
STO
Status information
R
ST'
after command
R ST 2
execution.
R C
Sector ID information
R H
after command
R R
execution.
R N
12 Diskette Adapter

Data Bus
Phase R/W
07 06 05 04 03 02 01 DO
Remarks
Recalibrate
Command W 0 0 0 0 0 1 1 1
Command Codes
W X X X X X 0
US1USO
Execution Head retracted
to
No Result track 0
Phase
Sense
Interrupt Status
Command
Result W
R
R
0 0 0 0 1
STO
PCN
0 0 0 Command Codes
Status
information at
the end of seek
operation
about the
FDC
Command
No Result
Phase
W
W
W
0
r---
0
SRT
Specify
0 0 0
HLT
0 1 1
HUT--
NO
Command Codes
Command
Result
W
W
R
0
X 0 X
Sense Drive
Status
0 0 0 1 0 0
X X X HDUS1USO
ST 3
Command Codes
Status
information
about FDD.
Command
Execution
W
W
W
0
X 0 X 0
X
Seek
0 1
X X
NCN
1 1 1
HDUS1USO
Command Codes
Head is positioned
over proper cylinder
on
diskette.
No Result
Phase
Command
W Invalid
Invalid Codes Invalid
command
codes (NoOp ~ FDC
goes
into standby
state).
Result R
STO
STO= 80.
Diskette Adapter 13

Bit
No. Name Symbol Description
07
07 = Oand06 = 0
Interrupt IC Normal termination of command (NT).
Code
Command was completed and properly
executed.
06
D7 = 0 and 06 = 1
Abnormal termination of command (AT).
Execution of command was started, but
was not successfully completed.
07 = 1 and 06 = 0
Invalid
command issue (IC). Command
that was issued was never started.
07 = 1 and 06 = 1
Abnormal termination because, during
command execution, the ready signal
from FOO changed state.
05 Seek End SE
When the FOC completes the seek
command, this flag is set to 1 (high).
04
Equipment
EC
If a fault signal is received from the
Check FOO,
or if the track 0 signal fails to occur
after 77 step pulses (recalibrate
command), then this flag is set.
03
Not Ready NR
When the FOO is in the not-ready state
and a read or write command is issued,
this flag is set. If a read or write command
is issued to side 1 of a single-sided drive,
then this flag is set.
02
Head Address HO
This flag is used to indicate the state of
the head at interrupt.
01
Unit Select 1 US 1 These flags are used to indicate a drive
00 Unit Select 0 usa unit number at interrupt.
Command Status Register 0
14 Diskette Adapter

Bit
No. Name
Symbol
Description
07
End of
EN When the FOC tries to access a sector
Cylinder beyond
the final sector of a cylinder. this
flag is set.
06
--
Not used. This bit is always 0 (low).
D5 Data Error
DE When the FDe detects a CRe error in
either the ID field or the data field. this
flag is set.
D4 Over Run
OR If the FDC is not serviced by the main
system during data transfers within a
certain time interval. this flag is set.
D3
--
Not used. This bit is always 0 (low).
D2 No Data
ND During execution of a read data. write
deleted data, or scan command. if the
FDC cannot find the sector specified in
the ID register. this flag is set. During
execution of the read ID command. if the
FDe cannot read the ID field without an
error,
then this flag is set. During the
execution of the read a cylinder
command, if the starting sector cannot be
found, then this flag is set.
01 Not Writable
NW During execution of a write data. write
deleted data. or format-a-cylinder
command. if the FDC detects a
write-protect signal from the FDO. then
this flag is set.
DO Missing
MA If the FDe cannot detect the ID address
Address
mark, this flag is set. Also. at the same
Mark
time, the MD (missing address mark in
the data field) of status register 2 is set.
Command Status Register 1
Diskette Adapter 15

Bit
No.
Name Symbol Description
D7
--
Not used. This bit is always 0 (low).
06 Control Mark CM During execution of the read data or scan
command, if the FDC encounters a sector
that contains a deleted data address
mark, this flag is set.
D5 Data Error in
DO
If the FDC detects a CRC error in the data,
Data Field
then this flag is set.
04
Wrong
WC
This bit is related to the ND bit, and when
Cylinder the contents of C on the medium are
different from that stored in the ID
register,
this flag is set.
D3 Scan Equal SH
During execution of the scan command, if
Hit the condition of "equal" is satisfied, this
flag is set.
D2 Scan Not
SN
During execution of the scan command,
Satisfied if the FDC cannot find a sector on the
cylinder that meets the condition, then
this flag is set.
D1 Bad Cylinder BC This bit is related to the ND bit, and when
the contents of C on the medium are
different from that stored in the ID
register, and
the contents of C is FF, then
this flag is set.
DO Missing MD When data is read from the medium, if
Address Mark
the FDC cannot find a data address mark
in Data Field or deleted data address mark.
then this
flag is set.
Command Status Register 2
16 Diskette Adapter