Tecnical manual, commands and controls (by intel)
Tecnical manual of the Intel 8272 FDD Controller Chip. A part from the general description of the chip, it contains diagrams and timing schemas, commands and function usage.
READ, WRITE, SEEK, RECALIBRATE, FORMAT TRACK are some of the explained commands.
This article is online from 2346 days and has been seen 10815 times
INTEL 8272
Single/Double Density Floppy Disk Controller
+ IBM Compatible in Both Single and + Data Transfers in DMA or Non-DMA
Double Density Recording Formats Mode
+ Programmable Data Record Lengths : + Parallel Seek Operations on Up to
128,256,512, or 1024 Bytes/Sector Four Drives
+ Drive Up to 4 Floppy Disks + Compatible with Most
Microprocessors Including 8080A,
+ Data Scan Capability - Will Scan a 8085A,8086 and 8088
Single Sector or an Entire Cylinder's
Worth of Data Fields, Comparing on a + Single-Phase 8 MHz Clock
Byte by Byte Basics, Data in the
Processor's Memory with Data Read + Single +5 Volt Power Supply
from the Diskette
+ Available in 40-Pin Plastic Dual-in
-line Package
The 8272 is an LSI Floppy Disk Controller (FDC) Chip, WHICH contains the
circulty and control functions for interfacing a processor to 4 Floppy Disk
Drives. It is capable of supporting either IBM 3740 single density format
(FM),or IBM System 34 Double Density format (MFM) including double sided
recording. The 8272 provides control signals which simlify the design of an
external phase locked loop, and write precompensation circultry. The FDC
simplifies and hanles most of the burdens associated with implementing
a Floppy Disk Drive Interface.
INDEX
-----
Pin Configuration
8272 Internal Block Diagram
8272 System Block Diagram
Description
Features
8272 Registers - Cpu Interface
Pin Description
Chip Commands
Polling Feature Of The 8272
Table 1. 8272 Command Set
Table 2. Command Mnemonics
Command Descriptions
Read Data
Table 3. Transfer Capacity
Table 4. Id Information When Processor Terminates Command
Write Data
Write Deleted Data
Read Deleted Data
Read A Track
Read Id
Format Track
Table 5. Sector Size Relationships
Scan Commands
Table 6. Scan Status Codes
Seek
Recalibrate
Sense Interrupt Status
Table 7. Seek Interrupt Codes
Specify
Sense Drive Status
Invalid
Table 8. Status Registers
_______________________________________________________________________________
PIN CONFIGURATION
+---+ +----+
RESET--+1 +---+ 40 +--Vcc
_RD--+2 39 +--_RW/SEEK
_WR--+3 38 +--LCT/DIR
_CS--+4 37 +--FR/STP
A0--+5 36 +--MDL
DB0--+6 35 +-RDY
DB1--+7 34 +--WP/TS
DB2--+8 33 +--FLT/TRK0
DB3--+9 32 +--PS0
DB4--+10 31 +--PS1
DB5--+11 30 +--WR DATA
DB6--+12 29 +--DS0
DB7--+13 28 +--DS1
DRQ--+14 27 +--HDSEL
_DACK--+15 26 +--MFM
TC--+16 25 +--WE
IDX--+17 24 +--Vc0
INT--+18 23 +--RD DATA
CLR--+19 22 +--DW
GND--+20 21 +--WR CLK
+------------+
8272 INTERNAL BLOCK DIAGRAM
! ! +----------+
+-------+ ! ! ! !
/__\ ! ! /__\ ! ! /__\ ! !
DB0-7<____>! DATA !<___ >!8!<____>! !
\ / ! BUS ! \ / !2! \ / !REGISTERS !
! BUFFER! !7! ! !
! ! !2! ! !
! ! ! ! ! !
+-------+ !I! ! !
-----+ !N! +----------+
TERMINAL ! !T!
COUNT \! / !E! +----------+
\/ !R! ! SERIAL !<------- WR CLOCK
+--------+ !N! ! INTERFACE!-------> WR DATA
DRQ<---! ! !A! /__\ !CONTROLLER!-------> WR ENABLE
DACK--->. READ ! !L!<____>! !-------> PRE-SHIFT0
INT<---! WRITE ! ! ! \ / ! !-------> PRE-SHIFT1
ID--->. DMA ! /__\ !B! ! !<------- READ DATA
WR--->. CONTROL!<____>!U! ! !<------- DATA WINDOW
A0--->! LOGIC ! \ / !S! +----------+-------> Vco SYNC
RESET--->! ! ! ! +----------+
! ! ! ! ! ! +-----+
+---.----+ ! ! ! ! /__! !
/!\ ! ! ! DRIVE !<___!INPUT!
! ! ! /__\ !INTERFACE ! \ ! PORT!
! ! !<____>!CONTROLLER! ! !
! ! ! \ / ! ! +-----+
CS -----+ ! ! ! ! /\ +-----+
! ! ! !<-->! !-->DRIVE SEL0
! ! +----------+ \/ ! OUT !-->DRIVE SEL1
! ! ! !-->MFM MODE
CLK ---> ! ! ! PORT!-->R/W SEEK
Vcc ---> ! !-->HEAD LOAD
GND ---> ! !-->HEAD SELECT
! !-->LOW
! ! CURRENT/DIRECTION
+-----+-->FAULT RESET/STEP
8272 SYSTEM BLOCK DIAGRAM
+------+
! !
! CPU !
! !
+------+
^
/ \
/ \
| |
| |
\ /
\ /
--------------------------------------------------------
SYSTEM BUS
--------------------------------------------------------
^ ^
/ \ / \
/ \ / \
| | | |
| | | |
\ / \ /
\ / \ /
+----------+ +----------+ DATA +---+ +----------+
! ! DRQ ! ! WINDOW ! ! ! --+
! !<--------! !<-----------!FLL!---! !
! ! ! ! ! ! | !
! 8237 ! ! 8272 ! +---+ | ! DRIVE !
! DMA ! _DACK ! ! RD DATA | ! !
!CONTROLLER!-------->! FDC !<------------------ !INTERFACE
! ! ! ! WR DATA ! !
! ! ! !------------------->! !
! ! ! ! / ! !
! !-------->! ! / -----------------! !
+----------+ TC ! !< INPUT CONTROL ! !
! ! \ -----------------! !
(TERMINAL COUNT)! ! \ ! !
! ! \ ! !
! !------------------\ ! !
! ! OUTPUT CONTROL >! !
+----------+------------------/ +----------+
/
DESCRIPTION
Hand-shaking signals are provided in the 8272 which make DMA operation
easy to incorporate with the aid of an external DMA Controller chip, such
as the 8237. The FDC will operate in einther DMA or Non-DMA mode. In the
Non-DMA mode,the FDC generates interrupts to the processor for every transfer
of data byte between the CPU and 8272. In the DMA mode, the processor need
only load command into the FDC and all data transfers occur under control of
the 8272 and DMA controller.
There are 15 separate commands which the 8272 will execute. Each of these
commands require multiple 8-bit bytes to fully specify the operation which
the processor wishes the FDC to perform. The following commands are available:
Read Data Write Data
Read ID Format a Track
Read Deleted Data Write Deleted Data
Read a Track Seek
Scan Equal Recalibrate (Restore to Track 0)
Scan High or Equal Sense Interrupt Status
Scan Low or Equal
Specify Sense Drive Status
FEATURES
Addres mark detection circultry is internal to the FDC which simlifies the
phase locked loop and read electronics. The track stopping rate, head load
time, and head unload time may be programmed by user. The 8272 offers many
additional features such as multiple sector transfers in both read and write
modes with a single command, and full IBM compatibillity in both single (FM)
and double density (MFM) modes.
8272 REGISTERS - CPU INTERFACE
The 8272 contain two registers which may accessed by the main system
processor: 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 consists of several registers in
a stack with only one register presented to the data bus at time), stores
data ,commands,parameters, and FDD status information. Data bytes are read
out of, or written into, the Data Register in order to program or obtain the
results after execution of command. The Status Register may only be read and
is used to facilitate the transfer of data between the processor and 8272.
The relationship between the Status/Data registers and the signals _RD,_WR,
and A0 is shown below.
+---+-----+-----+---------------------------+
!A0 ! _RD ! _WR ! FUNCTION !
+---+-----+-----+---------------------------+
! 0 ! 0 ! 1 ! Read Main Status !
! ! ! ! Register !
+---+-----+-----+---------------------------+
! 0 ! 1 ! 0 ! illegal !
+---+-----+-----+---------------------------+
! 0 ! 0 ! 0 ! illegal !
+---+-----+-----+---------------------------+
! 1 ! 0 ! 0 ! illegal !
+---+-----+-----+---------------------------+
! 1 ! 0 ! 1 ! Read from Data Register !
+---+-----+-----+---------------------------+
! 1 ! 1 ! 0 ! Write into Data Register !
! ! ! ! !
+---+-----+-----+---------------------------+
READY
-------+ NOT+------+ +---------+ +-----+ +-------¸
REQUEST ! ! ! ! ! ! ! ! !
FOR ! RDY! ! ! ! ! ! !
MASTER +----+ +--+ +----+ +------+ !
(RQM) ! ! !
! ! ! ! !
! ! !
! ! ! !
! ! ! ! !
! ! ! !
-----+ +----+----+ +--------------------------------------
_WR ! ! ! ! ! ! ! ! !
+-+ +-+ ! !
! ! ! ! ! ! !
-------+----+------+----------+ +--------+ +--------------
! ! ! ! ! ! ! ! ! ! !
_RD +-+ +-+
! ! ! ! ! ! !
! ! !
+----+----+------+--+----+----+----+-----+----+-+-------+
! A ! B ! A !B ! A ! C ! D ! C ! D !B! A !
+----+----+------+--+----+----+----+-----+----+-+-------+
NOTE : (A) - DATA REGISTER READY TO BE WRITTEN INTO BY PROCESSOR
(B) - DATA REGISTER NOT READY TO BE WRITTEN INTO AT PROCESSOR
(C) - DATA REGISTER READY FOR NEXR DATA BYTE TO BE READ BY THE
PROCESSOR.
(D) - DATA REGISTER NOT READY FOR NEXT DATA BYTE TO BE READ BY
PROCESSOR
Pic. STATUS REGISTER TIMING
CHIP COMMANDS
The 8272 is capable of executing 15 different commands. Each command is
initiated by a multi-byte transfer from the proaessor, and the result after
execution of the command may also be a multi-byte transfer back to the
processor. Because of this multi-byte interchange of information between
the 8272 and the processor, 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 processor.
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
processor.
During Command or Result Phases the Main Status Register (described earlier)
must be read by the processor before each byte of information is written into
or read from the Data Register. Bits D6 and D7 in the Main Status Register
must be in a 0 and 1 state, respectively,before each byte of the command word
may be written into the 8272. Many of the commands require multiple bytes,
and as a result the Main Status Register must be read prior to each byte
transfer to the 8272. On the other hand, during the Result Phase, D6 and D7
in the Main Status Register must both 1's (D6=1 and D7=1) before reading each
byte from the Data Register. Note, this reading of the Main Status Register
before each byte transfer to the 8272 is required in only the Command and
Result Phases, and NOT during the Execution Phase.
During the Execution Phase, the Main Status Register need not be read. If the
8272 is in the NON-DMA Mode, then the receipt of each data byte (if 8272 is
reading data from FDD) is indicated by an interrupt signal on pin 18 (INT=1).
The generation of Read signal (_RD=0) will reset the interrupt as well as
output the Data onto the Data Bus. For example, if the processor connot handle
interrupts fast enough (every 13 ms for MFM mode) then it may poll the Main
Status Register and then bit D7 (RQM) functions just like the interrupt signal.
If a Write Command is in process then the _WR signal performs the reset to the
interrupt signal.
If the 8272 is in the DMA Mode, no interrupts are generated during the
Execution Phase. The 8272 generated DRQ's (DMA Requests) when each byte of
data is available. The DMA Controller responds to this request with both a
_DACK =0 (DMA Acknowledge) and a _RD = 0 (Read signal).
When the DMA Acknowlege signal goes low (_DACK=0) then the DMA Request is
reset (DRQ=0). If a Write Command has been prorammed then a _WR signal will
appear instead of _RD. After the Execution Phase has been completed (Terminal
Count has occurred) then an interrupt will occur (INT=1). This signifies the
beginning of the Result Phase. When the first byte of data is read during the
Result Phase, the interrupt is automatically reset (INT=0).
It is important to note that during the Result Phase all bytes shown in the
Command Table must be read. The Read Data Command, for example, has seven
bytes of data in the Result Phase. All seven bytes must be read in order to
succesfully complete the Read Data Command. The 8272 will not accept a new
command until all seven bytes have been read. Other commands may require fewer
bytes to be read during the Result Phase.
The 8272 contains five Status Register. The Main Status Register mentioned
above may be read by the processor at any time. The other four Status
Registers (ST0,ST1,ST2, and ST3) are only available during the Result Phase,
and may be read only after successfully completing command. The particular
command which has been executed determines how many of the Status Register
will be read.
The bytes of data which are sent to the 8272 in the Result Phase, must occur
in the order shown in the Command Table. That is ,the Command Code must be
sent first and the other bytes sent in the prescribed sequence.
No foreshortening of the Command of Result Phases are allowed. After the last
byte of data in the Command Phase is sent to the 8272 the Execution Phase
automatically starts. In a similar fashion, when the last byte of data is read
out in the Result Phase, the command is automtically ended and the 8272 is
ready for a new command. Acommand may be aborted by simply sending a Terminal
Count to pin 16 (TC=1). This is convenient means of ensuring that the
processor may always get the 8272's attention even if the disk system hangs
up in an abnormal manner.
POLLING FEATURE OF THE 8272
After the Specify command has been sent to the 8272, the Drive Select Lines
DS0 and DS1 will automatically go into a polling mode. In between commands
(and between step pulses in the SEEK command) the 8272 polls all four FDD
looking for a change in the Ready line from any of the drives. If the Ready
line changes state (usually due to a door opening of closing) then the 8272
will generate an interrupt. When Status Register 0 (ST0) is read (after Sense
interrupt Status is issued), Not Ready (NR) will be indicated. The polling of
the Ready line by the 8272 occurs continuously between instructions, thus
notifying the processor which drives are on or off line.
COMMAND DESCRIPTIONS
During the Commnd Phase, the Main Status Register must be polled by the CPU
before each byte is written into the Data Register. The DIO (DB6) and RQM
(DB7) bits in the Main Status Register must be in the "0" and "1" states
respectivety, before each byte of the command may be written into the 8272.
The beginning of the execution phase for any of these commands will chuse
DIO and RQM to switch to "1" and "0" states respectively.
READ DATA
A set of nine (9) byte words are required to place the FDC into the Read Data
Mode. After the Read Data commands has been issued the FDC loads the head
(if it is in the unloaded state), waits the specified head setting time
(defined in the Specify Command), and begins reading ID Address Mark and ID
fields. When the current sector number ("R") stored in the ID Register (IDR)
compares with the sector number read off the diskette, then FDC outputs data
(from the data field) byte-byte to the main system via the data bus.
After completion of the read operatipn from the current sector, the Sector
Number is incremented by one , and the data from the next sector is read and
output on the data bus. This continuous read function is called a "Multi-
Sector Read Operation". The Read Data Command may be the receipt of a Terminal
Count signal. Upon receipt of this signal, the FDC stops outputting data to
the processor, but will continue to read data from the current sector, check
CRC (Cyclic Redundancy Count) bytes, and then at the end of the sector
terminate the Read Data Command.
The amount of data wchich can be hanled with a single command to the FDC
depends upon MT (multo-track), MFM (MFM/FM), and N (Number of Bytes/Sector).
Table 3 below shows the Transfer Capacity.
TABLE 3. TRANSFER CAPACITY
+-----------+-------+-------------+---------------------------------+---------+
!Multi-Track! MFM/FM! Bytes/Sector! Maximum Transfer Capacity ! Final !
! MT ! MFM ! N ! (Bytes/Sector)(Number of Sectors! Sector !
! ! ! ! ! Read !
! ! ! ! ! from !
! ! ! ! ! Diskette!
+-----------+-------+-------------+---------------------------------+---------+
! 0 ! 0 ! 00 ! (128)(26)=3.325 !26 at !
! 0 ! 1 ! 01 ! (256)(26)=6.656 !Side 0 or!
! ! ! ! !Side 1 !
+-----------+-------+-------------+---------------------------------+---------+
! ! ! ! ! !
! 1 ! 0 ! 00 ! (128)(52)=6.656 ! 26 !
! 1 ! 1 ! 01 ! (256)(52)=13.312 ! at Side1!
+-----------+-------+-------------+---------------------------------+---------+
! ! ! ! !Side 1 !
! 0 ! 0 ! 01 ! (256)(15)=3.840 ! or 0 !
! 0 ! 1 ! 02 ! (512)(15)=7.680 ! 15 !
+-----------+-------+-------------+---------------------------------+---------+
! ! ! ! ! 15 !
! 1 ! 0 ! 01 ! (256)(30)=7.680 ! at !
! 1 ! 1 ! 02 ! (512)(30)=15.360 !Side 1 !
+-----------+-------+-------------+---------------------------------+---------+
! ! ! ! !8 at Side!
! 0 ! 0 ! 02 ! (512)(8)=4.095 !0 or 8 at!
! 0 ! 1 ! 03 ! (1024)(8)=8.192 !Side 1 !
+-----------+-------+-------------+---------------------------------+---------+
! ! ! ! ! !
! 1 ! 0 ! 02 ! (512)(16)=8.192 !8 at !
! 1 ! 1 ! 03 ! (1024)(16)=16.384 !Side 1 !
! ! ! ! ! !
+-----------+-------+-------------+---------------------------------+---------+
The "multi-track" function (MT) allows the FDC to read data from sides of the
diskette. For a particular cylinder, data will be transferred starting at
Sector 1,Side 0 and completing at Sector L, Side 1 ( Sector L- last sector
on the side). Note, this function pertains to only one cylinder (the same
track ) on each side of the diskette.
When N=0, then DTL defines the length which the FDC must treat as a sector.
If DTL is smaller than the actual data length in a Sector, the data beyong DTL
in the Sector, is not sent to the Data Bus. The FDC reads (internally) the
complete Sector performing the CRC check, and depending upon the manner of
command termination, may perform a Multi-Sector Read Operation. When N is
no-zero, then DTL has no meaning and should be set to 0FFH.
At the completion of the Read Data Command, the head is not unloaded until
after Head Unload Time inteval (specified in the Specify Command) has elapsed.
If the processor issues another command before the head unloads then the head
setting time may be saved between subsequent reads. This time out is
particulary valuable when a diskette is copied from one drive to another.
If the FDC detects the Index Hole twice without finding the riht sector,
(indicated in "R"), then the FDC sets the ND (No Data) flag in Status Register
1 to a 1 (high), and terminates the Read Data Command. (Status Register 0 also
has bits 7 and 6 set to 0 and 1 respectively).
After reading the ID and Data Fields in each sector, the FDC checks the CRC
bytes . If a read error is detected (incorrect CRC in ID field), the FDC sets
the DE (Data Error) flag in Status Register 1 to a 1 (high), and if a CRC
error occurs in the Data Field the FDC also sets the DD(Data Error in Data
Field) flag in Status Register 2 to a 1 (high), and terminates the Read Data
Command. (Status Register 0 also has bits 7 and 6 set to 0 and 1 respectively)
If the FDC reads a Deleted Data Address Mark off the diskette, and the SK bit
(bit D5) in the first Command Word) is not set (SK=0), then the FDC sets the
CM (Control Mark) flag in Status Register 2 to a 1 (high), and terminates the
Read Data Command,after reading all the data in the Sector. If SK=1, the FDC
skips the sector with the Deleted Data Address Mark and reads the next sector.
During disk data transfers between the FDC and the processor, via data bus,
FDC must be serviced by the processor every 27 ms in the FM Mode, and every
13 ms in the MFM Mode, or the FDC sets the OR (Over Run) flag in Status
Register 1 to a 1 (high), and terminates the Read Data Command.
If the processor terminates a read (or write) operation in the FDC, then the
ID information in the Result Phase is dependent upon the state of the MT bit
and EOT byte. Table 4 shows the values for C,H,R, and N, when the processor
terminates the Command.
(*** download for full text ***)
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