Crawly Crypt Collection 1

home *** CD-ROM | disk | FTP | other *** search

/ Crawly Crypt Collection 1 / crawlyvol1.bin / program / hard_ref / theref / diagrams.doc < prev next >

Wrap

Text File | 1991-10-02 | 32KB | 408 lines

םגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגג™ ø DIAGRAMS.DOC Supplement to TheRef(tm) Drive & Controller Listing øõ בגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגœõ ø In "publishing" TheRef(tm), I've often been asked the difference øõ ø between the types of drive controllers and recording methods. I'm øõ ø not going to get into that in this document, as it would require a øõ ø good sized doc. of it's own. What I have supplied are diagrams of øõ ø the different connectors associated with the technology today. øõ ø frf øõ בגגגגגגגגגגגגגגגגגגגגגגגגגגגגœ CABLES בגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגœõ ø øõ ø Controller Drive 2(or none) Drive 1 øõ ø øõ ø 1חלל† גגגגגגגגג1חלל† גגגגstripeגגגגג1חלל† Pins 10-16 øõ ø FLOPPY cable ´::´≡≡≡≡≡≡≡≡≡≡≡´בœ´≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡´בœ´ are twisted øõ ø with twist ´::´≡≡≡≡≡≡≡≡≡≡≡´בœ´≡≡≡≡≡≡≡≡≡≡≡≡≡XX≡≡´בœ´ before the øõ ø (control & ´::´≡≡≡≡≡≡≡≡≡≡≡´בœ´≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡´בœ´ connector. øõ ø data, 34 pin) ´::´≡≡≡≡≡≡≡≡≡≡≡´בœ´≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡´בœ´ (7 wires) øõ ø זלל¶ זלל¶ זלל¶ øõ ø 1חלל† גגגגגגגגג1חלל† גגגגstripeגגגגג1חלל† Pins 25-29 øõ ø ST412 & ESDI ´::´≡≡≡≡≡≡≡≡≡≡≡´בœ´≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡´בœ´ are twisted øõ ø Hard Drive ´::´≡≡≡≡≡≡≡≡≡≡≡´בœ´≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡´בœ´ before the øõ ø cable w/twist ´::´≡≡≡≡≡≡≡≡≡≡≡´בœ´≡≡≡≡≡≡≡≡≡≡≡≡≡XX≡≡´בœ´ connector. øõ ø (control) ´::´≡≡≡≡≡≡≡≡≡≡≡´בœ´≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡´בœ´ (5 wires) øõ ø זלל¶ זלל¶ זלל¶ øõ ø 1חלל† גגגגגגגגגגגstripeגגגגגגגגגגגגג1חלל† (no twists) øõ ø ST412 & ESDI ´::´≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡´בœ´ Each drive øõ ø Hard Drive ´::´≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡´בœ´ has it's øõ ø (data, 20 pin)´::´≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡´בœ´ own data øõ ø זלל¶ זלל¶ cable øõ ø øõ ø IMPORTANT NOTE: Pin #1 on any drive cable SHOULD be indicated by a øõ ø a colored stripe. If you should find the stripe øõ ø by connector pin 34 (or 20), inspect the whole øõ ø cable VERY throughly! øõ ø øõ ø DRIVE SELECT For both Floppy and Hard drives, when the 34 pin øõ ø JUMPERS: cable has a twist, the device number should be set øõ ø to the second position. Drives numbered 0-3, set to øõ ø 1, those numbered 1-4, set to 2. When cables with- øõ ø out a twist are used, Floppy "A", and(or) Hard drive øõ ø "C" should be set to 1, and the second Floppy and øõ ø (or) Hard drive should be set to 2. øõ ø øõ ø TERMINATORS: When using more than one drive on a cable (ie; 2FDs øõ ø or 2HDs), the terminating resistor pack should be øõ ø left on the drive furthest from the controller, and øõ ø removed from the drive closest to the controller. øõ ø øõ ø NOTE: On SCSI drives, the Host Adapter also has resistors. øõ ø These are needed to terminate both ends of the bus. øõ ø Since the SCSI bus can have up to 7 devices attached øõ ø to it, only the Host Adapter and the device farthest øõ ø from it will retain the resistors. All devices in- øõ ø between should have theirs removed. øõ ĳגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגךõ õõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõ םגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגג™ ø DIAGRAMS.DOC 2 øõ בגגגגגגגגגגגגגגגגגגגגגגגגגגœ CONNECTIONS בגגגגגגגגגגגגגגגגגגגגגגגגגגגœõ ø øõ ø FLOPPY DRIVES םגגגגג™ øõ ø HI/LO DENSITY >ø2 1ø GND øõ ø The connector on a floppy drive N/C ø4 _ 3ø | øõ ø consists of 34 conductors. Both N/C ø6 5ø | øõ ø control and data use this same INDEX <ø8 7ø | øõ ø cable. Most cables have a twist MOTOR ENAB. A >ø10 9ø | øõ ø that interchanges pins 10 through DRIVE SEL. B >ø12 11ø | øõ ø 16 at the end of the cable (on DRIVE SEL. A >ø14 13ø | øõ ø drive 1). Most floppy connect- MOTOR ENAB. B >ø16 15ø | øõ ø ors have a "key" between pins DIRECTION SEL. >ø18 17ø | øõ ø 4 & 6, and 3 & 5, to prevent the HEAD STEP >ø20 19ø | øõ ø cable from being reversed. At WRITE DATA >ø22 21ø | øõ ø the other end, the dual row con- WRITE GATE >ø24 23ø | øõ ø nector that attaches to the con- TRACK 00 <ø26 25ø | øõ ø troller card will usually have a WRITE PROTECT <ø28 27ø | øõ ø set of ridges that coincide with READ DATA <ø30 29ø | øõ ø cutouts in the controller card's HEAD SELECT >ø32 31ø | øõ ø connector. Note that old style DISK CHANGE <ø34 33ø GND øõ ø floppy-only controllers used a ĳגגגגגך øõ ø card-edge connector just like that > Input ( At the øõ ø of the drive. < Output Drive Conn.) øõ ø øõ ø ST506/412 HARD DRIVE (MFM & RLL) øõ ø øõ ø This standard drive system uses םגגגגג™ øõ ø two cables; a 34 conductor control HEAD SEL. 8 ø2 1ø GND øõ ø cable, and a 20 conductor data HEAD SEL. 4 ø4 _ 3ø | øõ ø cable. The control cable contains WRITE GATE ø6 5ø | øõ ø a twist of the conductors going to SEEK COMPLETE ø8 7ø | øõ ø the farthest drive, which is drive TRACK 0 ø10 9ø | øõ ø "C" on most systems. This twist WRITE FAULT ø12 11ø | øõ ø consists of conductors 25 through HEAD SEL. 1 ø14 13ø | øõ ø 29. As with the floppy cable, the RESERVED ø16 15ø | øõ ø ST506/412 cables normally have a HEAD SEL. 2 ø18 17ø | øõ ø key to prevent reversal, and the INDEX ø20 19ø | øõ ø controller end has a pin-type con- READY ø22 21ø | øõ ø nector, while the drive end has a STEP ø24 23ø | øõ ø card-edge type connector. DRIVE SEL. 1 ø26 25ø | øõ ø DRIVE SEL. 2 ø28 27ø | øõ ø םגגגגג™ DRIVE SEL. 3 ø30 29ø | øõ ø DRIVE SEL'D ø1 2ø GND DRIVE SEL. 4 ø32 31ø | øõ ø RESERVED ø3 _ 4ø | DIRECTION IN ø34 33ø GND øõ ø | ø5 6ø | ĳגגגגגך øõ ø | ø7 8ø GND øõ ø RESERVED ø9 10ø RESERVED Though control signals øõ ø GND ø11 12ø GND go through a single 34 øõ ø * WRITE DATA+ ø13 14ø * WRITE DATA- conductor cable, data øõ ø GND ø15 16ø GND flows through seperate øõ ø * READ DATA+ ø17 18ø * READ DATA- 20 conductor cables øõ ø GND ø19 20ø GND for each drive (C,D). øõ ø *(MFM or RLL) ĳגגגגגך øõ ĳגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגךõ õõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõ םגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגג™ ø DIAGRAMS.DOC 3 øõ בגגגגגגגגגגגגגגגגגגגגגגגגגגœ CONNECTIONS בגגגגגגגגגגגגגגגגגגגגגגגגגגגœõ ø øõ ø ESDI HARD DRIVES םגגגגג™ øõ ø HEAD SEL. 3 ø2 1ø GND øõ ø Though ESDI and ST506/412 drives HEAD SEL. 2 ø4 _ 3ø | øõ ø share similar looking cables, WRITE GATE ø6 5ø | øõ ø even to the point of having a CONFIG/STAT DATA ø8 7ø | øõ ø twist, the actual data and con- TRANSFER ACK. ø10 9ø | øõ ø trol signals are very different. ATTENTION ø12 11ø | øõ ø One should never mix components HEAD SEL. 0 ø14 13ø | øõ ø from these two drive types. SECT/ADD.MK. FOUND ø16 15ø | øõ ø While the ST506/412 interface HEAD SEL. 1 ø18 17ø | øõ ø utilizes a standard pulse code INDEX ø20 19ø | øõ ø to transmit data between the READY ø22 21ø | øõ ø drive and controller, ESDI uses TRANS.REQUEST ø24 23ø | øõ ø a pulse code that does not require DRIVE SEL. 1 ø26 25ø | øõ ø the level to return to zero between DRIVE SEL. 2 ø28 27ø | øõ ø pulses. This format is refered to DRIVE SEL. 3 ø30 29ø | øõ ø as NRZ, or Non Return to Zero. By READ GATE ø32 31ø | øõ ø utilizing NRZ, the clock that data COMMAND DATA ø34 33ø GND øõ ø is transfered by can be increased, ĳגגגגגך øõ ø thereby increasing the troughput to øõ ø and from the ESDI disk. øõ ø םגגגגג™ øõ ø DRIVE SEL'D ø1 2ø SECT/ADD.MK. FOUND øõ ø SEEK COMPLETE ø3 4ø ADDRESS MARK ENABLE øõ ø RESV'D FOR STEP MODE ø5 6ø GND øõ ø WRITE CLOCK+ ø7 8ø WRITE CLOCK- øõ ø CARTRIDGE CHANGED ø9 10ø READ REF. CLOCK+ øõ ø READ REF. CLOCK- ø11 12ø GND øõ ø NRZ WRITE DATA+ ø13 14ø NRZ WRITE DATA- øõ ø GND ø15 16ø GND øõ ø NRZ READ DATA+ ø17 18ø NRZ READ DATA- øõ ø GND ø19 20ø GND øõ ø ĳגגגגגך øõ ø øõ ø גגגגגגגגגגגגגגג™ And in this corner... Recording םגגגגגגגגגגגגגגגג øõ ø øõ ø Times were, you had a simple choice for type of disk drive... øõ ø Any kind, as long as it was ST506/412. Those were the heydays of øõ ø MFM drives. But many manufacturers weren't content with the 17 øõ ø sectors/track that MFM provided. They devised a newer encoding øõ ø scheme to pack data tighter, and called it RLL, or Run Length øõ ø Limited, as opposed to MFM, or Modified Frequency Modulation. It øõ ø involves using groups of 16 bits rather than each individual bit, øõ ø thus achieving a sort of "compression" of the information as it is øõ ø encoded. Since the same information takes up less space as RLL øõ ø encoded data, more info can be writen to the disk. The most com- øõ ø mon RLL technique, known as 2,7 RLL, can pack roughly 50% more on øõ ø a disk than MFM. Of course, there is always a trade-off, and the øõ ø timing and media required for RLL is it. RLL requires a higher øõ ø grade of media because of it's dense bit-packing, and timing is øõ ø more critical, since the data is flowing at 50% higher rate than øõ ø an MFM drive. Also, the mechanics of the drive must have tighter øõ ĳגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגךõ õõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõ םגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגג™ ø DIAGRAMS.DOC 4 øõ בגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגœõ ø tolerences because head positioning becomes more critical. These øõ ø requirements kept RLL drives at a premium. It has only been the øõ ø last two years, that RLL drives have outsold MFM, and have all but øõ ø wiped them from the marketplace. This turnabout has come from the øõ ø need to increase disk capacity more and more. Both ESDI, and SCSI øõ ø type drives utilize RLL.(1*) encoding to achieve high capacity and øõ ø transfer rates (from the disk). And the newest interface, IDE, or øõ ø Integrated Drive Electronics, is also based on this technology. øõ ø גגגגגגגגגגגגגגגגגגגגגגגגגגגגגגג™ םגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגג øõ ø םגגגגג™ øõ ø SCSI HARD DRIVES DB0 <>ø2 1ø GND 5 øõ ø DB1 <>ø4 3ø | 0 øõ ø The normal internal cable for SCSI DB2 <>ø6 5ø | øõ ø is a 50 conductor ribbon, with all DB3 <>ø8 7ø | P øõ ø odd numbered conductors grounded. DB4 <>ø10 9ø | I øõ ø Two conductors, numbers 25 & 26, are DB5 <>ø12 11ø | N øõ ø often left not-connected, as they DB6 <>ø14 13ø | øõ ø deal with Terminator power, and can DB7 <>ø16 15ø | D øõ ø be easily shorted by cable reversals. DBP <>ø18 17ø | U øõ ø There are no twists in this cable, GND ø20 19ø | A øõ ø and it's length may be a maximum of GND ø22 21ø | L øõ ø 6 meters. But one is advised to use GND ø24 23ø | øõ ø minimum lengths to improve timing. TERM PWR ø26 25ø | R øõ ø Up to seven drives, or devices may be GND ø28 27ø | O øõ ø attached to an SCSI cable. Each is GND ø30 29ø | W øõ ø daisy-chained on the cable, or, when ATN >ø32 31ø | øõ ø a device has two connectors, another GND ø34 33ø | C øõ ø cable may be "spliced" into the chain BSY <>ø36 35ø | O øõ ø starting at the second connector, and ACK >ø38 37ø | N øõ ø continued on. Care must be taken to RST <>ø40 39ø | N øõ ø insure that cables and connectors are MSG < ø42 41ø | E øõ ø not reversed, as this would short pin SEL <>ø44 43ø | C øõ ø 26 (TERMPWR) to ground, and likely C/D < ø46 45ø | T øõ ø damage the drive or controller. Also, REQ < ø48 47ø | O øõ ø as explained earlier, the terminating I/O < ø50 49ø GND R øõ ø resistors should remain only on the ĳגגגגגך øõ ø controller (Host Adapter) and the LAST םגג™ DB-25F CONN. øõ ø drive on the cable, regardless of it's GND ø1 ĳגג™ øõ ø address. DB1 <>ø2 14ø<> DB0 øõ ø Most SCSI Host Adapters also have DB3 <>ø3 15ø<> DB2 øõ ø a connector for external drives in the DB5 <>ø4 16ø<> DB4 øõ ø form of a Centronics(tm) type 50 pin, DB7 <>ø5 17ø<> DB6 øõ ø or an "alternate", DB-25F connector. GND ø6 18ø<> PARITY øõ ø Only the internal 50-pin, and the SEL <>ø7 19ø GND øõ ø "alternate" external connector are GND ø8 20ø< ATN øõ ø shown here. (see also: MORE SCSI) TMPWR ø9 21ø > MSG øõ ø Also, these diagrams refer to the RST <>ø10 22ø< ACK øõ ø single-ended SCSI connections, since C/D < ø11 23ø<> BSY øõ ø this is the most common arrangement I/O < ø12 24ø > REQ øõ ø for PCs today. The Differential SCSI GND ø13 25ø GND øõ ø requires balanced lines, and is used ø םגגך øõ ø mostly on high-end workstations. ĳגגך FUTURE DOMAINøõ ĳגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגךõ õõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõ םגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגג™ ø DIAGRAMS.DOC 5 øõ בגגגגגגגגגגגגגגגגגגגגגגגגגגגגœ CABLES בגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגœõ ø SCSI (cont.) øõ ø (T) םג(DC)™ (T) øõ ø On an SCSI cable, the 1חלל†גstripeג1חלל†גג1חלל†גג1חללילל†גג1חלל† øõ ø terminating resistors ´::´≡≡≡≡≡≡≡≡≡´::´≡≡≡´::´≡≡≡´::´::´≡≡≡´::´ øõ ø (T) remain at the END ´::´≡≡≡≡≡≡≡≡≡´::´≡≡≡´::´≡≡≡´::´::´≡≡≡´::´ øõ ø devices on the cable, ´::´≡≡≡≡≡≡≡≡≡´::´≡≡≡´::´≡≡≡´::´::´≡≡≡´::´ øõ ø even when 2 cables are ´::´≡≡≡≡≡≡≡≡≡´::´≡≡≡´::´≡≡≡´::´::´≡≡≡´::´ øõ ø "Daisy-Chained" (DC). ´::´≡≡≡≡≡≡≡≡≡´::´≡≡≡´::´≡≡≡´::´::´≡≡≡´::´ øõ ø Also, the external ´::´≡≡≡≡≡≡≡≡≡´::´≡≡≡´::´≡≡≡´::´::´≡≡≡´::´ øõ ø connector may be used, זלל¶ זלל¶ זלל¶ זללטלל¶ זלל¶ øõ ø requiring the removal (HA) Drives 1-7 (in any order) øõ ø of the Host Adapter's øõ ø internal Term. resistors. øõ בגגגגגגגגגגגגגגגגגגגגגגגגגגœ CONNECTORS בגגגגגגגגגגגגגגגגגגגגגגגגגגגגœõ ø øõ ø IDE (AT) HARD DRIVES (<> AT THE DRIVE CONN) øõ ø םגגגגג™ øõ ø IDE, or Integrated Drive Electronics RST >ø1 2ø GND øõ ø is the most recent drive interface to SD7 <>ø3 4ø<> SD8 øõ ø gain popularity. Often, the control SD6 <>ø5 6ø<> SD9 øõ ø circuitry is built into the mother- SD5 <>ø7 8ø<> SD10 øõ ø board, eliminating the requirement for SD4 <>ø9 10ø<> SD11 øõ ø a seperate Host Adapter. There are 2 SD3 <>ø11 12ø<> SD12 øõ ø types of IDE interfaces...those for the SD2 <>ø13 14ø<> SD13 øõ ø 8-bit XT bus, and those for the 16-bit SD1 <>ø15 16ø<> SD14 øõ ø AT bus (detailed here). The cable for SD0 <>ø17 18ø<> SD15 øõ ø IDE contains 40 conductors and has no GND ø19 20øN/C (KEY) øõ ø twists. Like an SCSI cable, the IDE RES.N/Cø21 22ø GND øõ ø cable uses a Dual-row Pin connector for IOW >ø23 24ø GND øõ ø both ends. A single cable may be used IOR >ø25 26ø GND øõ ø to connect two drives, or two cables RES.N/Cø27 28øN/C RES. øõ ø may be Daisy-Chained. Most IDE Host RES.N/Cø29 30ø GND øõ ø Adapters will support two hard drives. IRQ14 <ø31 32ø> I/O CS16 øõ ø The first drive should be jumpered as SA1 <>ø33 34ø<> PDIAG øõ ø the Master drive, and the second as the SA0 <>ø35 36ø<> SA2 øõ ø Slave drive. Plug-in IDE Host Adapters CS0 >ø37 38ø< CS1 øõ ø are often called Paddle-Boards, and ACTIVE <ø39 40ø GND øõ ø may contain a floppy controller, and ĳגגגגגך øõ ø serial and parallel ports. øõ ø øõ בגגגגגגגגגגגגגגגגגגגגגגגגגגגגœ CABLES בגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגœõ ø Note: øõ ø 1חלל†גגגגstripeגגגגג1חלל†גגגגגגגגגגג1חלל† øõ ø The IDE Host Adapter ´::´≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡´::´≡≡≡≡≡≡≡≡≡≡≡≡´::´ øõ ø connector may be on ´::´≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡´::´≡≡≡≡≡≡≡≡≡≡≡≡´::´ øõ ø a plug-in Paddle-Board ´::´≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡´::´≡≡≡≡≡≡≡≡≡≡≡≡´::´ øõ ø or may be integrated ´::´≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡´::´≡≡≡≡≡≡≡≡≡≡≡≡´::´ øõ ø on the Motherboard. ´::´≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡´::´≡≡≡≡≡≡≡≡≡≡≡≡´::´ øõ ø זלל¶ זלל¶ זלל¶ øõ ø Host Adapter Drives 1-2 (any order) øõ בגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגœõ ø 1* There ARE some SCSI drives that utilize MFM, but very few. øõ ĳגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגךõ õõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõ םגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגג™ ø DIAGRAMS.DOC 6 øõ בגגגגגגגגגגגגגגגגגגגגגגג™ More on Recording םגגגגגגגגגגגגגגגגגגגגגגגגœõ ø øõ ø WRITE PRECOMPENSATION øõ ø øõ ø OK, so we've all seen it listed, and maybe even had to set it øõ ø in the CMOS. So what IS it? And what does it do? øõ ø PreComp. is the way in which the electronics compensates for øõ ø eventual "drift" of the magnetic domains written on the disk. A øõ ø simple explaination is that it allows the head to space bits that øõ ø would attract each other, further apart, while it puts those that øõ ø repel each other, closer together. It does this by analyzing the øõ ø data stream, and adjusting the timing for each bit, to allow it to øõ ø be recorded earlier or later, if needed. øõ ø Not all disks require you to set their PreComp value. Those øõ ø that do are asking for a cylinder to start PreComp. at. Since the øõ ø packing of the bits on a disk increases as you get closer to the øõ ø center of the disk (higher cylinders), the requirement for PreComp.øõ ø increases too. The PreComp. value specified by the Manufacturer øõ ø for a disk is his way of insuring your long term data stability. øõ ø øõ ø גג< THE EFFECT OF PRECOMPENSATION OVER TIME >גג øõ ø øõ ø When recorded (w/o PreComp) When recorded (with PreComp) øõ ø םגגגגגגגגגגגגגגגגגגגגגגגגגגגגגג™ םגגגגגגגגגגגגגגגגגגגגגגגגגגגגגג™ øõ ø ø +- -+ +- +- -+ -+ ø ø +- -+ +- -+ -+ -+ø øõ ø ĳגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגך ĳגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגך øõ ø øõ ø After time (w/o PreComp) After time (with PreComp) øõ ø םגגגגגגגגגגגגגגגגגגגגגגגגגגגגגג™ םגגגגגגגגגגגגגגגגגגגגגגגגגגגגגג™ øõ ø ø+- -+ +- +- -+ -+ ø ø +- -+ +- -+ -+ -+ ø øõ ø ĳגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגך ĳגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגך øõ ø øõ ø From the figures above, we can see how a slight amount of Pre- øõ ø Compensation can insure long term stability. The disk that didn't øõ ø employ PreComp was eventually unreadable. Of course, this would øõ ø take time to happen, but no one can give cold hard specs on how øõ ø much drift will occure. (Of course, this example is a gross sim- øõ ø plification of the process, but, hey, who's counting?) øõ ø øõ בגגגגגגגגגגגגגגגגגגגגגגגœ For Notes & Such בגגגגגגגגגגגגגגגגגגגגגגגגגœõ ø øõ ø øõ ø øõ ø øõ ø øõ ø øõ ø øõ ø øõ ø øõ ø øõ ø øõ ø øõ ø øõ ĳגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגךõ õõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõ םגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגג™ ø DIAGRAMS.DOC 7 øõ בגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגœõ ø APPLE SCSI øõ ø øõ ø Unlike in the PC world, the Apple APPLE DB-25 SCSI øõ ø standardized on one drive interface, םגגגג™ øõ ø SCSI. Also, Apple standardized on REQ < ø1 ĳ™ øõ ø a 25 pin connector for external con- MSG < ø2 14ø GND øõ ø nections. However, Apple decided not I/O < ø3 15ø > C/D øõ ø to implement the complete ANSI spec., RST <>ø4 16ø GND øõ ø so one must be careful that peripherals ACK >ø5 17ø< ATN øõ ø used are certified to work with Apple's BSY <>ø6 18ø GND øõ ø SCSI bus. GND ø7 19ø<> SEL øõ ø Apple also developed it's own pin- DB0 <>ø8 20ø<> PARITY øõ ø configuration. The Apple and Future GND ø9 21ø<> DB1 øõ ø Domain 25-pin SCSI connectors are as DB3 <>ø10 22ø<> DB2 øõ ø close to "Standards" as there are in DB5 <>ø11 23ø<> DB4 øõ ø the world of PCs. But the real ANSI DB6 <>ø12 24ø GND øõ ø Standard called for a 50 pin connector DB7 <>ø13 25ø TMPWR øõ ø commonly referred to as a "Centronics" ø םך øõ ø type (made popular by the Centronics ĳגגגגך øõ ø printer company). Instead of the 25 øõ ø staggered pins of the Apple & Future 50-PIN "CENTRONICS" øõ ø Domain type connectors, the Centronics TYPE SCSI øõ ø type uses 2 parallel rows of 25 pins. םגגגגג™ øõ ø This arrangement allowed use of extra ø1 26ø øõ ø grounds for better isolation. ø2 27ø øõ ø ø3 28ø øõ ø ø4 29ø øõ ø ø5 30ø øõ ø ø6 31ø øõ ø ø7 32ø øõ ø ø8 33ø øõ ø (WORK IN PROGRESS) ø9 34ø øõ ø ø10 35ø øõ ø ø11 36ø øõ ø ø12 37ø øõ ø ø13 38ø øõ ø ø14 39ø øõ ø ø15 40ø øõ ø ø16 41ø øõ ø ø17 42ø øõ ø ø18 43ø øõ ø ø19 44ø øõ ø ø20 45ø øõ ø ø21 46ø øõ ø ø22 47ø øõ ø ø23 48ø øõ ø ø24 49ø øõ ø ø25 50ø øõ ø ĳגגגגגך øõ ø øõ ø øõ ø THE END? øõ ĳגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגגךõ õõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõõ⇧