X3T9.2/87-169 Rev 1 Nov. 16, 1987 To: X3T9.2 Committee (SCSI) From: Gerry Houlder MPI/CDC Subject: Pinouts for double density alternative 2 connector Rev. 1 Changes: Add description for expansion to 8 bytes wide, add appendix describing 100 pin to 50 pin isolator module. This proposal suggests an easy way to upgrade to a 2 byte wide SCSI bus while remaining within the form factor of the existing alternative 2 connector (also known as the ribbon connector). A third data byte also fits in the connector and an expansion cable contains a fourth byte to achieve 4 byte wide transfers. The advantages of this idea are as follows: * The double density ribbon connector provides for 100 pins in the same connector housing as the existing 50 pin connector described in Appendix D. This proposal adds lines for 16 data lines, 2 parity lines, a 50PIN SENSE line to detect connection of a 50 pin connector with the 100 pin connector, and 2 more TERMPWR pins. An expansion connector is defined to accommodate more data bytes plus REQB and ACKB signals. This allows migration to 4 or 8 byte wide transfers. * The existing ribbon connector is the most popular shielded connector for SCSI. It makes sense to remain compatible with an accepted shielded option when many users of a 2 byte wide SCSI will use external peripheral subsystems. * The double density connector can mate with the existing 50 pin ribbon connector without harming system operation. The system cannot operate in 2 byte wide mode, but the current 1 byte wide SCSI can still operate. The 50PIN SENSE signal detects the 50 pin connector and disables the extra signals in the same way that DIFFSENS disables the differential drivers if a single-ended device is connected to the SCSI bus. * Cables made with the 100 pin connector can be used with devices that use the existing 50 pin connector. The resulting use of 2 wires in the cable for each of the 50 contacts lowers the resistance of the cable and the redundant wire and contact increases the reliability (because one bad contact or one bad wire won't break the connection). Shielded, round cable with 50 pairs of 28 ga. wire is only slightly larger (.50 in. dia.) than a cable with 25 pairs of 28 ga. wire (.42 in. dia.) and it is just as flexible. * The addition of a second data byte to the interface will double the maximum data transfer rate and stay within one cable. With the expansion cable, 4 or 8 byte wide transfers are possible. * The increased data rate of 2 byte wide transfers is achieved without increasing the amount of real estate required for the connector. More room will probably be required by the extra circuitry for the additional interface lines, however. This is the most space effective proposal so far to accommodate two byte wide data transfers. * The existing Wide SCSI Transfer message can still allow each peripheral to negotiate for 1, 2, 4, or 8 byte wide transfers as desired. * This proposal includes pinouts for both differential and single-ended driver options. * The 100 pin connector was estimated to cost $5.00. This is significantly below the estimated $15.00 cost for some of the micro-miniature connectors also being considered. There are some disadvantages that must be noted, however. They are listed here: - A different terminator is required for the 100 pin versus the 50 pin style. Further, this terminator cannot also terminate SCSI devices that use the 50 pin connector. - Because of the terminator differences, 50 pin devices can not be randomly interspersed with 100 pin devices on the same bus. If the 50 pin devices were all at the same end of the bus, however, a 100 pin to 50 pin isolator module (similar to an in- line terminator) will allow coexistence. An isolator module would pass through the 50 original SCSI signals and provide termination resistors (as needed) for the 50 expansion signals. A "50 pin terminator" would be at one end of the bus and a "100 pin terminator" would be at the other end. Note: The "100 pin terminator" could consist of an isolator module with a "50 pin terminator" plugged onto it. See appendix for details of the isolator module. Pinouts for differential and single-ended versions of the 100 pin connector are on the following pages. The pinouts maintain the existing pin numbers and shows the additional pins as a "B" suffix of the pin that it would be shorted to if a 50 pin connector were mated to the 100 pin connector. The actual connector probably won't be numbered this way, but this makes it easier to visualize potential problems of mating a 50 pin connector with the 100 pin connector. The new signals in the cables are as follows: DB lines - Data lines 8 through 23 and parity lines P1 and P2 are added. These lines are validated by the existing REQ and ACK lines during wide data phase transfers. 50PINSENS (50 pin Connector Sense) line - This connects to a circuit like in Figure 4-8 of the SCSI-2 draft. When a 50 pin connector is plugged into a 100 pin connector, the connection to GROUND causes the circuit to disable any drivers on the DB 8-23, P1, and P2 lines. BCABLSENS (B Cable Sense) - This also connects to a circuit like in Figure 4-8 of the SCSI-2 draft. When an A cable is plugged into a B cable connector, the connection to GROUND causes the circuit to disable all drivers on both cables. There are good reasons for choosing the pinouts suggested in the following diagrams. * The DIFFSENS pin would be shorted to a "no connect" if a 50 pin connector was mated to the 100 pin connector. This assures that the DIFFSENS line works properly even if a 50 pin connector were attached. * The 50PINSENS pin would short to ground. This is required for this pin to do its job properly. If it doesn't disable the drivers for data bits 8-23, P1, and P2, they could be damaged by being connected to ground or a driver for another signal. * The BCABLESENS pin connects to ground if an A cable is plugged into a B cable connector. This provides protection against misplugging cables without resorting to keyed cables. * The existing GROUND pins would short to another ground. This minimizes the chances of damaging a driver when a 50 pin connector is mated. * The existing TERMPWR would short to another TERMPWR line. If it shorted to anything else, an overcurrent condition can result. This also offers two additional pins to handle current requirements of the TERMPWR. This should fix the 5 amp current limit problem brought up by Bill Spence of TI. The extra pins mean that 28 ga wire is enough to handle the maximum current without needing 26 ga wire to meet CSA requirements. Cable A - shielded - Differential Pin Assignments Signal Name Pin Number Signal Name ----------------------------------------------------------------- GROUND 1 26 GROUND GROUND 1B 26B GROUND +DB(0) 2 27 -DB(0) +DB(8) 2B 27B -DB(8) +DB(1) 3 28 -DB(1) +DB(9) 3B 28B -DB(9) +DB(2) 4 29 -DB(2) +DB(10) 4B 29B -DB(10) +DB(3) 5 30 -DB(3) +DB(11) 5B 30B -DB(11) +DB(4) 6 31 -DB(4) +DB(12) 6B 31B -DB(12) +DB(5) 7 32 -DB(5) +DB(13) 7B 32B -DB(13) +DB(6) 8 33 -DB(6) +DB(14) 8B 33B -DB(14) +DB(7) 9 34 -DB(7) +DB(15) 9B 34B -DB(15) +DB(P) 10 35 -DB(P) +DB(P1) 10B 35B -DB(P1) -DIFFSENS 11 36 GROUND NO CONNECT 11B 36B -50PINSENS GROUND 12 37 GROUND GROUND 12B 37B GROUND TERMPWR 13 38 TERMPWR TERMPWR 13B 38B TERMPWR GROUND 14 39 GROUND GROUND 14B 39B GROUND +ATN 15 40 -ATN +DB(16) 15B 40B -DB(16) GROUND 16 41 GROUND NO CONNECT 16B 41B NO CONNECT +BSY 17 42 -BSY +DB(17) 17B 42B -DB(17) +ACK 18 43 -ACK +DB(18) 18B 43B -DB(18) +RST 19 44 -RST +DB(19) 19B 44B -DB(19) +MSG 20 45 -MSG +DB(20) 20B 45B -DB(20) +SEL 21 46 -SEL +DB(21) 21B 46B -DB(21) +C/D 22 47 -C/D +DB(22) 22B 47B -DB(22) +REQ 23 48 -REQ +DB(23) 23B 48B -DB(23) +I/O 24 49 -I/O +DB(P2) 24B 49B -DB(P2) GROUND 25 50 GROUND GROUND 25B 50B GROUND ================================================================= Cable A - shielded - Single-Ended Pin Assignments Signal Pin Number ----------------------------------------------------------------- -DB(0) 26 -DB(8) 26B -DB(1) 27 -DB(9) 27B -DB(2) 28 -DB(10) 28B -DB(3) 29 -DB(11) 29B -DB(4) 30 -DB(12) 30B -DB(5) 31 NOTE: Pins 13 and 13B -DB(13) 31B shall be left open. -DB(6) 32 Pins 1-12, 1B-12B, -DB(14) 32B 14-25, and 14B-25B -DB(7) 33 shall be connected -DB(15) 33B to ground. -DB(P) 34 -DB(P1) 34B GROUND 35 GROUND 35B GROUND 36 -50PINSENS 36B GROUND 37 GROUND 37B TERMPWR 38 TERMPWR 38B GROUND 39 GROUND 39B GROUND 40 GROUND 40B -ATN 41 -DB(16) 41B GROUND 42 NO CONNECT 42B -BSY 43 -DB(17) 43B -ACK 44 -DB(18) 44B -RST 45 -DB(19) 45B -MSG 46 -DB(20) 46B -SEL 47 -DB(21) 47B -C/D 48 -DB(22) 48B -REQ 49 -DB(23) 49B -I/O 50 -DB(P2) 50B ================================================================= Cable B - shielded - Differential Pin Assignments Signal Name Pin Number Signal Name ----------------------------------------------------------------- +DB(24) 1 26 -DB(24) +DB(25) 1B 26B -DB(25) +DB(26) 2 27 -DB(26) +DB(27) 2B 27B -DB(27) +DB(28) 3 28 -DB(28) +DB(29) 3B 28B -DB(29) +DB(30) 4 29 -DB(30) +DB(31) 4B 29B -DB(31) +DB(P3) 5 30 -DB(P3) +REQB 5B 30B -REQB +ACKB 6 31 -ACKB +DB(32) 6B 31B -DB(32) +DB(33) 7 32 -DB(33) +DB(34) 7B 32B -DB(34) +DB(35) 8 33 -DB(35) +DB(36) 8B 33B -DB(36) +DB(37) 9 34 -DB(37) +DB(38) 9B 34B -DB(38) +DB(39) 10 35 -DB(39) +DB(P4) 10B 35B -DB(P4) +DIFFSENS 11 36 +BCABLSENS +DB(40) 11B 36B -DB(40) +DB(41) 12 37 -DB(41) +DB(42) 12B 37B -DB(42) TERMPWR 13 38 TERMPWR TERMPWR 13B 38B TERMPWR +DB(43) 14 39 -DB(43) +DB(44) 14B 39B -DB(44) +DB(45) 15 40 -DB(45) +DB(46) 15B 40B -DB(46) +DB(47) 16 41 -DB(47) +DB(P5) 16B 41B -DB(P5) +DB(48) 17 42 -DB(48) +DB(49) 17B 42B -DB(49) +DB(50) 18 43 -DB(50) +DB(51) 18B 43B -DB(51) +DB(52) 19 44 -DB(52) +DB(53) 19B 44B -DB(53) +DB(54) 20 45 -DB(54) +DB(55) 20B 45B -DB(55) +DB(P6) 21 46 -DB(P6) +DB(56) 21B 46B -DB(56) +DB(57) 22 47 -DB(57) +DB(58) 22B 47B -DB(58) +DB(59) 23 48 -DB(59) +DB(60) 23B 48B -DB(60) +DB(61) 24 49 -DB(61) +DB(62) 24B 49B -DB(62) +DB(63) 25 50 -DB(63) +DB(P7) 25B 50B -DB(P7) ================================================================= Cable B - shielded - Single-Ended Pin Assignments Signal Pin Number ----------------------------------------------------------------- -DB(24) 26 -DB(25) 26B -DB(26) 27 -DB(27) 27B -DB(28) 28 -DB(29) 28B -DB(30) 29 -DB(31) 29B -DB(P3) 30 -REQB 30B -ACKB 31 NOTE: Pins 13 and 13B -DB(32) 31B shall be left open. -DB(33) 32 Pins 1-12, 1B-12B, -DB(34) 32B 14-25, and 14B-25B -DB(35) 33 shall be connected -DB(36) 33B to ground. -DB(37) 34 -DB(38) 34B -DB(39) 35 -DB(P4) 35B +BCABLSENS 36 -DB(40) 36B -DB(41) 37 -DB(42) 37B TERMPWR 38 TERMPWR 38B -DB(43) 39 -DB(44) 39B -DB(45) 40 -DB(46) 40B -DB(47) 41 -DB(P5) 41B -DB(48) 42 -DB(49) 42B -DB(50) 43 -DB(51) 43B -DB(52) 44 -DB(53) 44B -DB(54) 45 -DB(55) 45B -DB(P6) 46 -DB(56) 46B -DB(57) 47 -DB(58) 47B -DB(59) 48 -DB(60) 48B -DB(61) 49 -DB(62) 49B -DB(63) 50 -DB(P7) 50B ================================================================= Appendix A - 100 pin to 50 pin isolator module description. This appendix describes an isolator module that allows a 100 pin SCSI bus (like that described in this proposal) to be connected to an existing 50 pin SCSI bus. The connection scheme allows all devices to communicate in one byte wide mode and allows the devices on the 100 pin part of the bus to communicate in a wider bus mode if desired. A differential SCSI version is described but the same principles apply to a single-ended version also. __________________ ______________ ______________ | 1||1 isolator 5||5 5| | 0||0 module 0||0 terminator 0| | SCSI device 0||0_____________||______________| |(100 pin conn.) | ___ | 1||1 |______ | 0||0 |____ | |_________________0||0__| | | cable #1 | | __________________ ___ | | | 1||1 |____| | | 0||0 |______| | SCSI device 0||0__| (100 pin conn.) | ______________ ___ | 1||1 isolator 5||5 |_____ | 0||0 module 0||0 |___ | |_________________0||0_____________||___| | | | | __________________ ___ cable #2 | | | 5||5 |___________________| | | 0||0 |_____________________| | SCSI device ||___| | (50 pin conn.) | ___ | 5||5 |______ | 0||0 |____ | |__________________||___| | | | | cable #3 __________________ ___ | | | 5||5 |____| | | 0||0 |______| | SCSI device ||___| | (50 pin conn.) | ______________ | 5||5 5| | 0||0 terminator 0| |__________________||______________| For this example system, cable #1 must be 100 conductor cable and cables #2 and #3 can be either 50 conductor cable or 100 conductor cable. Using 100 conductor cable throughout the system can help eliminate cabling problems. The system uses 2 isolator modules and two 50 pin terminator modules like those available from Amphenol. An isolator module can be implemented in a package similar in size to the Amphenol terminator module. The following pages are a schematic showing internal connections for a differential SCSI isolator module. The "3 terminator resistor" blocks are the same as shown in figure 4-6 of the SCSI- 2 draft. Items marked "to GROUND" are connected together and items marked "to TERMPWR" are also connected together within the isolator module. The general idea of the design is to pass through the "original 50" signals from the 100 pin connector to the 50 pin connector, provide proper termination for the new signals (the 2nd and 3rd data bytes), and provide proper connections to ground and terminator power. 100 pin conn. 50 pin conn. ------------- ------------ 1 >--------*----------*-------------------------*-----< 1 26 >-------/ \--- to GROUND \----< 26 1B >------/ 26B >-----/ 2 >---------------------------------------------------< 2 27 >---------------------------------------------------< 27 _____________ 2B >-----------| 3 terminator|--- to TERMPWR 27B >-----------|__resistors__|--- to GROUND 3 >---------------------------------------------------< 3 28 >---------------------------------------------------< 28 _____________ 3B >-----------| 3 terminator|--- to TERMPWR 28B >-----------|__resistors__|--- to GROUND 4 >---------------------------------------------------< 4 29 >---------------------------------------------------< 29 _____________ 4B >-----------| 3 terminator|--- to TERMPWR 29B >-----------|__resistors__|--- to GROUND 5 >---------------------------------------------------< 5 30 >---------------------------------------------------< 30 _____________ 5B >-----------| 3 terminator|--- to TERMPWR 30B >-----------|__resistors__|--- to GROUND 6 >---------------------------------------------------< 6 31 >---------------------------------------------------< 31 _____________ 6B >-----------| 3 terminator|--- to TERMPWR 31B >-----------|__resistors__|--- to GROUND 7 >---------------------------------------------------< 7 32 >---------------------------------------------------< 32 _____________ 7B >-----------| 3 terminator|--- to TERMPWR 32B >-----------|__resistors__|--- to GROUND 8 >---------------------------------------------------< 8 33 >---------------------------------------------------< 33 _____________ 8B >-----------| 3 terminator|--- to TERMPWR 33B >-----------|__resistors__|--- to GROUND 9 >---------------------------------------------------< 9 34 >---------------------------------------------------< 34 _____________ 9B >-----------| 3 terminator|--- to TERMPWR 34B >-----------|__resistors__|--- to GROUND 10 >---------------------------------------------------< 10 35 >---------------------------------------------------< 35 _____________ 10B >-----------| 3 terminator|--- to TERMPWR 35B >-----------|__resistors__|--- to GROUND 11 >---------------------------------------------------< 11 36 >--------------------------------*------------------< 36 11B >----------- no connection \--- to GROUND 36B >----------- no connection 12 >--------*----------*-------------------------*-----< 12 37 >-------/ \--- to GROUND \----< 37 12B >------/ 37B >-----/ 13 >--------*---*--------------------------------*-----< 13 38 >-------/ \--- to TERMPWR \----< 38 13B >------/ 38B >-----/ 14 >--------*----------*-------------------------*-----< 14 39 >-------/ \--- to GROUND \----< 39 14B >------/ 39B >-----/ 15 >---------------------------------------------------< 15 40 >---------------------------------------------------< 40 _____________ 15B >-----------| 3 terminator|--- to TERMPWR 40B >-----------|__resistors__|--- to GROUND 16 >--------*----------*-------------------------*-----< 16 41 >-------/ \--- to GROUND \----< 41 16B >----------- no connection 41B >----------- no connection 17 >---------------------------------------------------< 17 42 >---------------------------------------------------< 42 _____________ 17B >-----------| 3 terminator|--- to TERMPWR 42B >-----------|__resistors__|--- to GROUND 18 >---------------------------------------------------< 18 43 >---------------------------------------------------< 43 _____________ 18B >-----------| 3 terminator|--- to TERMPWR 43B >-----------|__resistors__|--- to GROUND 19 >---------------------------------------------------< 19 44 >---------------------------------------------------< 44 _____________ 19B >-----------| 3 terminator|--- to TERMPWR 44B >-----------|__resistors__|--- to GROUND 20 >---------------------------------------------------< 20 45 >---------------------------------------------------< 45 _____________ 20B >-----------| 3 terminator|--- to TERMPWR 45B >-----------|__resistors__|--- to GROUND 21 >---------------------------------------------------< 21 46 >---------------------------------------------------< 46 _____________ 21B >-----------| 3 terminator|--- to TERMPWR 46B >-----------|__resistors__|--- to GROUND 22 >---------------------------------------------------< 22 47 >---------------------------------------------------< 47 _____________ 22B >-----------| 3 terminator|--- to TERMPWR 47B >-----------|__resistors__|--- to GROUND 23 >---------------------------------------------------< 23 48 >---------------------------------------------------< 48 _____________ 23B >-----------| 3 terminator|--- to TERMPWR 48B >-----------|__resistors__|--- to GROUND 24 >---------------------------------------------------< 24 49 >---------------------------------------------------< 49 _____________ 24B >-----------| 3 terminator|--- to TERMPWR 49B >-----------|__resistors__|--- to GROUND 25 >--------*----------*-------------------------*-----< 25 50 >-------/ \--- to GROUND \----< 50 25B >------/ 50B >-----/