��������������������������������������������������������������������Ŀ � DIAGRAMS.DOC Supplement to TheRef(tm) Drive & Controller Listing �� ��������������������������������������������������������������������Ĵ� � 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 �� ����������������������������Ĵ CABLES ������������������������������Ĵ� � �� � Controller Drive 2(or none) Drive 1 �� � �� � 1��ͻ ���������1��ͻ ����stripe�����1��ͻ Pins 10-16 �� � FLOPPY cable �::������������ô������������������ô� are twisted �� � with twist �::������������ô��������������XX��ô� before the �� � (control & �::������������ô������������������ô� connector. �� � data, 34 pin) �::������������ô������������������ô� (7 wires) �� � ��ͼ ��ͼ ��ͼ �� � 1��ͻ ���������1��ͻ ����stripe�����1��ͻ Pins 25-29 �� � ST412 & ESDI �::������������ô������������������ô� are twisted �� � Hard Drive �::������������ô������������������ô� before the �� � cable w/twist �::������������ô��������������XX��ô� connector. �� � (control) �::������������ô������������������ô� (5 wires) �� � ��ͼ ��ͼ ��ͼ �� � 1��ͻ �����������stripe�������������1��ͻ (no twists) �� � ST412 & ESDI �::���������������������������������ô� Each drive �� � Hard Drive �::���������������������������������ô� has it's �� � (data, 20 pin)�::���������������������������������ô� own data �� � ��ͼ ��ͼ 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. �� ���������������������������������������������������������������������ٱ ���������������������������������������������������������������������� ��������������������������������������������������������������������Ŀ � DIAGRAMS.DOC 2 �� ��������������������������Ĵ CONNECTIONS ���������������������������Ĵ� � �� � FLOPPY DRIVES �����Ŀ �� � 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 �����Ŀ �� � 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� | �� � �����Ŀ 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) ������� �� ���������������������������������������������������������������������ٱ ���������������������������������������������������������������������� ��������������������������������������������������������������������Ŀ � DIAGRAMS.DOC 3 �� ��������������������������Ĵ CONNECTIONS ���������������������������Ĵ� � �� � ESDI HARD DRIVES �����Ŀ �� � 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. �� � �����Ŀ �� � 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 �� � ������� �� � �� � ��������������Ŀ 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 �� ���������������������������������������������������������������������ٱ ���������������������������������������������������������������������� ��������������������������������������������������������������������Ŀ � DIAGRAMS.DOC 4 �� ��������������������������������������������������������������������Ĵ� � 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. �� � ������������������������������Ŀ ��������������������������������� �� � �����Ŀ �� � 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 ��Ŀ DB-25F CONN. �� � drive on the cable, regardless of it's GND �1 ��Ŀ �� � 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�� ���������������������������������������������������������������������ٱ ���������������������������������������������������������������������� ��������������������������������������������������������������������Ŀ � DIAGRAMS.DOC 5 �� ����������������������������Ĵ CABLES ������������������������������Ĵ� � SCSI (cont.) �� � (T) ��(DC)� (T) �� � On an SCSI cable, the 1��ͻ�stripe�1��ͻ��1��ͻ��1�����ͻ��1��ͻ �� � 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, ��ͼ ��ͼ ��ͼ �����ͼ ��ͼ �� � requiring the removal (HA) Drives 1-7 (in any order) �� � of the Host Adapter's �� � internal Term. resistors. �� ��������������������������Ĵ CONNECTORS ����������������������������Ĵ� � �� � IDE (AT) HARD DRIVES (<> AT THE DRIVE CONN) �� � �����Ŀ �� � 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. �� � �� ����������������������������Ĵ CABLES ������������������������������Ĵ� � Note: �� � 1��ͻ����stripe�����1��ͻ�����������1��ͻ �� � The IDE Host Adapter �::�����������������::�������������::� �� � connector may be on �::�����������������::�������������::� �� � a plug-in Paddle-Board �::�����������������::�������������::� �� � or may be integrated �::�����������������::�������������::� �� � on the Motherboard. �::�����������������::�������������::� �� � ��ͼ ��ͼ ��ͼ �� � Host Adapter Drives 1-2 (any order) �� ��������������������������������������������������������������������Ĵ� � 1* There ARE some SCSI drives that utilize MFM, but very few. �� ���������������������������������������������������������������������ٱ ���������������������������������������������������������������������� ��������������������������������������������������������������������Ŀ � DIAGRAMS.DOC 6 �� �����������������������Ŀ More on Recording ������������������������Ĵ� � �� � 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) �� � ������������������������������Ŀ ������������������������������Ŀ �� � � +- -+ +- +- -+ -+ � � +- -+ +- -+ -+ -+� �� � �������������������������������� �������������������������������� �� � �� � After time (w/o PreComp) After time (with PreComp) �� � ������������������������������Ŀ ������������������������������Ŀ �� � �+- -+ +- +- -+ -+ � � +- -+ +- -+ -+ -+ � �� � �������������������������������� �������������������������������� �� � �� � 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?) �� � �� �����������������������Ĵ For Notes & Such �������������������������Ĵ� � �� � �� � �� � �� � �� � �� � �� � �� � �� � �� � �� � �� � �� ���������������������������������������������������������������������ٱ ���������������������������������������������������������������������� ��������������������������������������������������������������������Ŀ � DIAGRAMS.DOC 7 �� ��������������������������������������������������������������������Ĵ� � APPLE SCSI �� � �� � Unlike in the PC world, the Apple APPLE DB-25 SCSI �� � standardized on one drive interface, ����Ŀ �� � 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 ���Ŀ �� � type uses 2 parallel rows of 25 pins. � �Ŀ �� � 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 �� ���������������������������������������������������������������������ٱ ���������������������������������������������������������������������� ��������������������������������������������������������������������Ŀ � DIAGRAMS.DOC 8 �� ��������������������Ŀ CONSTRUCTION PROJECT ������������������������Ĵ� � 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 ������������������������������Ŀ �� � for the Workstation market, not � 1 �/\/\/\/� 26 �/\/\/\/Ŀ � �� � the PC market. We may see these � 2 �/\/\/\/� 27 �/\/\/\/Ĵ � �� � prices erode as more PCs adopt � 3 �/\/\/\/� 28 �/\/\/\/Ĵ � �� � SCSI as their disk interface of � 4 �/\/\/\/� 29 �/\/\/\/Ĵ � �� � choice, but for now be prepared � 5 �/\/\/\/� 30 �/\/\/\/Ĵ � �� � to pay a premium for anything to � 6 �/\/\/\/� 31 �/\/\/\/Ĵ � �� � do with SCSI. � 7 �/\/\/\/� 32 �/\/\/\/Ĵ � �� � So here you are, with a disk � 8 �/\/\/\/� 33 �/\/\/\/Ĵ � �� � drive mounted internally, and a � 9 �/\/\/\/� 34 �/\/\/\/Ĵ � �� � 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 ��������Ĵ � �� � You've checked the connectors, and� 14 39 � � �� � everything looks good... So what's� 15 40 � � �� � the problem? Well, did you check � 16 �/\/\/\/� 41 �/\/\/\/Ĵ � �� � the terminators? (Say Whaaat??) � 17 42 � � �� � Improper termination of an SCSI � 18 �/\/\/\/� 43 �/\/\/\/Ĵ � �� � bus can raise havock with the Host� 19 �/\/\/\/� 44 �/\/\/\/Ĵ � �� � Adapter's interface circuit, and � 20 �/\/\/\/� 45 �/\/\/\/Ĵ � �� � result in missing peripherals, or � 21 �/\/\/\/� 46 �/\/\/\/Ĵ � �� � intermittent operation and pos- � 22 �/\/\/\/� 47 �/\/\/\/Ĵ � �� � sible loss of data. � 23 �/\/\/\/� 48 �/\/\/\/Ĵ � �� � Well, here's a way to build an � 24 �/\/\/\/� 49 �/\/\/\/Ĵ � �� � 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. �� ��������������������������������������������������������������������Ĵ� � �� � �� � �� � �� � (This space left unintentionally blank!) �� � �� � �� � �� � �� ���������������������������������������������������������������������ٱ ����������������������������������������������������������������������