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? DIAGRAMS.DOC Supplement to TheRef(tm) Drive & Controller Listing ??
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? 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 ?::????????????????????????????????????? are twisted ??
? with twist ?::?????????????????????????????XX?????? before the ??
? (control & ?::????????????????????????????????????? connector. ??
? data, 34 pin) ?::????????????????????????????????????? (7 wires) ??
? ???? ???? ???? ??
? 1???? ?????????1???? ????stripe?????1???? Pins 25-29 ??
? ST412 & ESDI ?::????????????????????????????????????? are twisted ??
? Hard Drive ?::????????????????????????????????????? before the ??
? cable w/twist ?::?????????????????????????????XX?????? connector. ??
? (control) ?::????????????????????????????????????? (5 wires) ??
? ???? ???? ???? ??
? 1???? ???????????stripe?????????????1???? (no twists) ??
? ST412 & ESDI ?::????????????????????????????????????? Each drive ??
? Hard Drive ?::????????????????????????????????????? has it's ??
? (data, 20 pin)?::????????????????????????????????????? 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 ?2 1? GND ??
? cable, and a 20 conductor data HEAD SEL. 4 ?4 _ 3? | ??
? cable. The control cable contains WRITE GATE ?6 5? | ??
? a twist of the conductors going to SEEK COMPLETE ?8 7? | ??
? the farthest drive, which is drive TRACK 0 ?10 9? | ??
? "C" on most systems. This twist WRITE FAULT ?12 11? | ??
? consists of conductors 25 through HEAD SEL. 1 ?14 13? | ??
? 29. As with the floppy cable, the RESERVED ?16 15? | ??
? ST506/412 cables normally have a HEAD SEL. 2 ?18 17? | ??
? key to prevent reversal, and the INDEX ?20 19? | ??
? controller end has a pin-type con- READY ?22 21? | ??
? nector, while the drive end has a STEP ?24 23? | ??
? card-edge type connector. DRIVE SEL. 1 ?26 25? | ??
? DRIVE SEL. 2 ?28 27? | ??
? ??????? DRIVE SEL. 3 ?30 29? | ??
? DRIVE SEL'D ?1 2? GND DRIVE SEL. 4 ?32 31? | ??
? RESERVED ?3 _ 4? | DIRECTION IN ?34 33? 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 ?2 1? GND ??
? Though ESDI and ST506/412 drives HEAD SEL. 2 ?4 _ 3? | ??
? share similar looking cables, WRITE GATE ?6 5? | ??
? even to the point of having a CONFIG/STAT DATA ?8 7? | ??
? twist, the actual data and con- TRANSFER ACK. ?10 9? | ??
? trol signals are very different. ATTENTION ?12 11? | ??
? One should never mix components HEAD SEL. 0 ?14 13? | ??
? from these two drive types. SECT/ADD.MK. FOUND ?16 15? | ??
? While the ST506/412 interface HEAD SEL. 1 ?18 17? | ??
? utilizes a standard pulse code INDEX ?20 19? | ??
? to transmit data between the READY ?22 21? | ??
? drive and controller, ESDI uses TRANS.REQUEST ?24 23? | ??
? a pulse code that does not require DRIVE SEL. 1 ?26 25? | ??
? the level to return to zero between DRIVE SEL. 2 ?28 27? | ??
? pulses. This format is refered to DRIVE SEL. 3 ?30 29? | ??
? as NRZ, or Non Return to Zero. By READ GATE ?32 31? | ??
? utilizing NRZ, the clock that data COMMAND DATA ?34 33? 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 ??
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? 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 ?::???????????::?????::?????::?::?????::? ??
? (T) remain at the END ?::???????????::?????::?????::?::?????::? ??
? devices on the cable, ?::???????????::?????::?????::?::?????::? ??
? even when 2 cables are ?::???????????::?????::?????::?::?????::? ??
? "Daisy-Chained" (DC). ?::???????????::?????::?????::?::?????::? ??
? Also, the external ?::???????????::?????::?????::?::?????::? ??
? 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 ?::??????????????????::??????????????::? ??
? connector may be on ?::??????????????????::??????????????::? ??
? a plug-in Paddle-Board ?::??????????????????::??????????????::? ??
? or may be integrated ?::??????????????????::??????????????::? ??
? on the Motherboard. ?::??????????????????::??????????????::? ??
? ???? ???? ???? ??
? 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 ??
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? 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 ??
? Domain type connectors, the Centronics ????? ??
? type uses 2 parallel rows of 25 pins. ? ??? ??
? This arrangement allows the use of extra GND ?1 26?<> DB0 ??
? grounds for better isolation. ? ?2 27?<> DB1 ??
? ? ?3 28?<> DB2 ??
? SCSI HISTORY ? ?4 29?<> DB3 ??
? ? ?5 30?<> DB4 ??
? SCSI has it's roots in the mainframe ? ?6 31?<> DB5 ??
? world, but it's first implementation in ? ?7 32?<> DB6 ??
? the PC world came soon after the first ? ?8 33?<> DB7 ??
? PC. Shugart Associates devised an inter- ? ?9 34?<> DBP ??
? face that they designated the SASI, or ? ?10 35? GND ??
? "Shugart Associates Standard Interface" ? ?11 36? GND ??
? They proposed that SASI be adopted by ANSI ? ?12 37? GND ??
? for small computers, but durring the work ? ?13 38? TERM.PWR. ??
? required for ratification, they discovered ? ?14 39? GND ??
? the process would take too much effort, and ? ?15 40? GND ??
? that the IPI groups were already well into ? ?16 41? > ATN ??
? their effort. (which had many features the ? ?17 42? GND ??
? same as SASI) A decision was made to take ? ?18 43?<> BSY ??
? features of both interfaces, and put forth ? ?19 44? > ACK ??
? a new specification for a new interface, ? ?20 45?<> RST ??
? SCSI was born, and ratified in 1986 by ? ?21 46?< MSG ??
? ANSI. Since then, many have said that the ? ?22 47?<> SEL ??
? original spec. was not tight enough, and ? ?23 48?< C/D ??
? that it allowed Manufacturers to make ? ?24 49?< REQ ??
? drives that met the ANSI spec., but would GND ?25 50?< I/O ??
? not talk to each other. Recently, the ? ??? ??
? ANSI SCSI committee has proposed newer, ????? ??
? tighter, more extended specs., for 50 PIN "CENTRONICS" ??
? SCSI-2, and now SCSI-3. FOR "PC" TYPE COMPUTERS ??
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? DIAGRAMS.DOC 8 ??
?????????????????????? CONSTRUCTION PROJECT ???????????????????????????
? SCSI TERMINATION ??
? ??
? With the advent of increased use of SCSI for peripherals comes ??
? the chance that one day you'll need an SCSI terminating resistor. ??
? Prepare for a shock, because you might be very suprised at the ??
? prices charged, for what you get. Many Manufacturers still have ??
? SCSI peripheral hardware priced ???????????????????????????????? ??
? for the Workstation market, not ? 1 ?/\/\/\/? 26 ?/\/\/\/?? ? ??
? the PC market. We may see these ? 2 ?/\/\/\/? 27 ?/\/\/\/?? ? ??
? prices erode as more PCs adopt ? 3 ?/\/\/\/? 28 ?/\/\/\/?? ? ??
? SCSI as their disk interface of ? 4 ?/\/\/\/? 29 ?/\/\/\/?? ? ??
? choice, but for now be prepared ? 5 ?/\/\/\/? 30 ?/\/\/\/?? ? ??
? to pay a premium for anything to ? 6 ?/\/\/\/? 31 ?/\/\/\/?? ? ??
? do with SCSI. ? 7 ?/\/\/\/? 32 ?/\/\/\/?? ? ??
? So here you are, with a disk ? 8 ?/\/\/\/? 33 ?/\/\/\/?? ? ??
? drive mounted internally, and a ? 9 ?/\/\/\/? 34 ?/\/\/\/?? ? ??
? CDRom hanging off the back of the ? 10 35 ? ? ??
? PC. Everything looks great, but ? 11 36 ? ? ??
? it just doesn't work... Maybe it ? 12 37 ? ? ??
? doesn't even recognize the CDRom. ? 13 38 ?????????? ? ??
? You've checked the connectors, and? 14 39 ? ? ??
? everything looks good... So what's? 15 40 ? ? ??
? the problem? Well, did you check ? 16 ?/\/\/\/? 41 ?/\/\/\/?? ? ??
? the terminators? (Say Whaaat??) ? 17 42 ? ? ??
? Improper termination of an SCSI ? 18 ?/\/\/\/? 43 ?/\/\/\/?? ? ??
? bus can raise havock with the Host? 19 ?/\/\/\/? 44 ?/\/\/\/?? ? ??
? Adapter's interface circuit, and ? 20 ?/\/\/\/? 45 ?/\/\/\/?? ? ??
? result in missing peripherals, or ? 21 ?/\/\/\/? 46 ?/\/\/\/?? ? ??
? intermittent operation and pos- ? 22 ?/\/\/\/? 47 ?/\/\/\/?? ? ??
? sible loss of data. ? 23 ?/\/\/\/? 48 ?/\/\/\/?? ? ??
? Well, here's a way to build an ? 24 ?/\/\/\/? 49 ?/\/\/\/?? ? ??
? inexpensive terminator that will ? 25 ?/\/\/\/? 50 ?/\/\/\/?? ? ??
? connect to the second SCSI con- ? 220? 330? ? ??
? nector on many SCSI peripherals. ???????????????????????????????? ??
? All you need is a Male 50-pin SCSI Terminator Schematic ??
? Centronics type connector, a small ??
? length of wire, and 18 resistors of 330? and 18 of 220?, 1/4 watt. ??
? The schematic for connecting the resistors & connector is above, ??
? and I'll not go any deeper into construction except to say that if ??
? you can't take it from here without explaination, you should buy ??
? your terminator instead, as you can do too much damage if you do it??
? wrong. ??
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? ??
? ??
? ??
? ??
? (This space left unintentionally blank!) ??
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