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