| 词条 | Floppy-disk controller | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 释义 |
A floppy-disk controller (FDC) is a special-purpose chip and associated disk controller circuitry that directs and controls reading from and writing to a computer's floppy disk drive (FDD). This article contains concepts common to FDCs based on the NEC µPD765 and Intel 8272A or 82072A and their descendants, as used in the IBM PC and compatibles from the 1980s and 1990s. The concepts may or may not be applicable to, or illustrative of, other controllers or architectures. OverviewA single floppy-disk controller (FDC) board can support up to four floppy disk drives. The controller is linked to the system bus of the computer and appears as a set of I/O ports to the CPU. It is often also connected to a channel of the DMA controller. On the x86 PC the floppy controller uses IRQ 6, on other systems other interrupt schemes may be used. The floppy disk controller usually performs data transmission in direct memory access (DMA) mode. The diagram below shows a floppy disk controller which communicates with the CPU via an Industry Standard Architecture (ISA) bus or similar bus and communicates with the Floppy Disk drive with a 34 pin ribbon cable. An alternative arrangement which is more usual in recent designs has the FDC included in a super I/O chip which communicates via a Low Pin Count (LPC) bus. Most of the floppy disk controller (FDC) functions are performed by the integrated circuit but some are performed by external hardware circuits. The list of functions performed by each is given below. Floppy disk controller functions (FDC)
External hardware functions
Input/output ports for common x86-PC controllerThe FDC has three I/O ports. These are:
The first two reside inside the FDC IC while the Control port is in the external hardware. The addresses of these three ports are as follows.
Data portThis port is used by the software for three different purposes:
Main status register (MSR)This port is used by the software to read the overall status information regarding the FDC IC and the FDD's. Before initiating a floppy disk operation the software reads this port to confirm the readiness condition of the FDC and the disk drives to verify the status of the previously initiated command. The different bits of this register represent :
Digital control portThis port is used by the software to control certain FDD and FDC IC functions. The bit assignments of this port are:
Interface to the floppy disk driveThe controller connects to the drive using a flat ribbon cable with 34 connectors split between the host, the 3.5" drive, and the 5.25" drive. This type of cable is called a universal connector.[1] In the IBM PC family and compatibles, a twist in the cable is used to distinguish disk drives by the socket to which they are connected. All drives are installed with the same drive select address set, and the twist in the cable interchange the drive select line at the socket. The drive that is at furthest end of the cable additionally would have a terminating resistor installed to maintain signal quality.[2]
Further description of the interface signals are contained in specifications of the controllers or drives[3]. Format data{{main|List of floppy disk formats}}Many mutually incompatible floppy disk formats are possible; aside from the physical format on the disk, incompatible file systems are also possible.
Sides:
Density:
{{anchor|3mode}}"3-mode" floppy drivePrimarily in Japan there are 3.5" high-density floppy drives that support three modes of disk formats instead of the normal two – 1440 KB (2 MB unformatted), 1.2 MB (1.6 MB unformatted) and 720 kB (1 MB unformatted). Originally, the high-density mode for 3.5" floppy drives in Japan only supported a capacity of {{nowrap|1.2 MB}} instead of the {{nowrap|1440 KB}} capacity that was used elsewhere.[14] While the more common 1440 KB format spun at 300 rpm, the 1.2 MB format instead spun at 360 rpm, thereby closely resembling the 1.2 MB format with 15 sectors per track previously found on 5.25" high-density floppy drives. Later Japanese floppy drives incorporated support for both high-density formats (as well as the double-density format), hence the name 3-mode. Some BIOSes have a configuration setting to enable this mode for floppy drives supporting it.[15] See also
References1. ^{{cite web |last1=Davis |first1=Larry |title=Floppy Drive Pinout, Signal names, Pin out Description and Cable twist wiring |url=http://www.interfacebus.com/PC_Floppy_Drive_PinOut.html |website=www.interfacebus.com |accessdate=January 29, 2019 |date=June 13, 2015}} 2. ^ Scott Mueller, Upgrading and Repairing PCs, Second Edition, Que, 1992, {{ISBN|0-88022-856-3}},page 487 3. ^hypertextbook.com – Angular Speed of a Floppy Disk 4. ^{{cite web|title=C 64 Workshop / C= 8 Bit & Peripherals|date=1998-05-19 |accessdate=2016-04-18|url=https://ist.uwaterloo.ca/~schepers/MJK/1541__.html}} 5. ^1 2 3 4 5 {{Cite web |url=http://diuf.unifr.ch/pai/education/2005_2006/courses/os/minix/idx/S/sys%20src%20kernel%20floppy.c.html |title=unifr.ch – sys/src/kernel/floppy.c |access-date=5 May 2011 |archive-url=https://web.archive.org/web/20110719150025/http://diuf.unifr.ch/pai/education/2005_2006/courses/os/minix/idx/S/sys%20src%20kernel%20floppy.c.html |archive-date=19 July 2011 |dead-url=yes |df=dmy-all }} 6. ^1 {{cite web|url=http://www.colorcomputerarchive.com/coco/Documents/Manuals/Hardware/Tandon%20TM100%20Floppy%20Drive%20(Tandon).pdf|title=Product specification single-sided and double-sided TM100 series 5 1/4-inch flexible disk drives 48, 96, and 100 tracks per inch|accessdate=2014-11-05}} 7. ^1 iesleonardo.info – This diskette tutorial provides technical information concerning diskettes 8. ^1 oldskool.org – Let HD 5,25" FDDs operate at 300 rpm instead of 360 rpm 9. ^1 intel.com – Intel 82077SL for Super Dense Floppies {{webarchive|url=https://web.archive.org/web/20121008000235/http://download.intel.com/design/archives/periphrl/docs/29209302.pdf |date=8 October 2012 }} 10. ^{{cite web |url=http://www.retrotechnology.com/herbs_stuff/drive.html#data |title=Floppy Drive Tech Info |author-last=Johnson |author-first=Herbert R. |date=2016-12-22 |access-date=2017-01-14}} 11. ^yi.org – High Density Floppy Disks Mf2hd Disk 3 5 1 Pk{{dead link|date=October 2017 |bot=InternetArchiveBot |fix-attempted=yes }} 12. ^mcamafia.de – IBM Personal system/2, 3,5"-inch Diskette Drives, Technical Reference 13. ^{{cite web|title=Linux-2.6.17/drivers/block/floppy.c|url=http://www.gelato.unsw.edu.au/lxr/source/drivers/block/floppy.c}}{{dead link|date=October 2017 |bot=InternetArchiveBot |fix-attempted=yes }} 090504 gelato.unsw.edu.au 14. ^[https://books.google.com/books?id=BIplH6DHz6UC&pg=PA509&lpg=PA509 books.google.com – Fix Your Own PC by Corey Sandler] 15. ^[https://web.archive.org/web/20041028094210/http://www.rojakpot.com/default.aspx?location=8&var1=0&var2=89 rojakpot.com – 3mode floppy support]
Further reading
External links
3 : Computer storage devices|Floppy disk computer storage|Integrated circuits |
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