Alasir Enterprises
Main Page >  Motley >  MicroHouse PC Hardware Library Volume I: Hard Drives  

 
Previous Table of Contents Next

 
Table 2.6  A-Cable (Single-Ended) External Shielded Connector.

Signal Name Pin Pin Signal Name

GROUND 1 26 -DB(0)
GROUND 2 27 -DB(1)
GROUND 3 28 -DB(2)
GROUND 4 29 -DB(3)
GROUND 5 30 -DB(4)
GROUND 6 31 -DB(5)
GROUND 7 32 -DB(6)
GROUND 8 33 -DB(7)
GROUND 9 34 -DB(Parity)
GROUND 10 35 GROUND
GROUND 11 36 GROUND
RESERVED 12 37 RESERVED
Open 13 38 TERMPWR
RESERVED 14 39 RESERVED
GROUND 15 40 GROUND
GROUND 16 41 -ATN
GROUND 17 42 GROUND
GROUND 18 43 -BSY
GROUND 19 44 -ACK
GROUND 20 45 -RST
GROUND 21 46 -MSG
GROUND 22 47 -SEL
GROUND 23 48 -C/D
GROUND 24 49 -REQ
GROUND 25 50 -I/O

IBM has standardized on the SCSI interface for virtually all PS/2 systems introduced since 1990. These systems use a Micro-Channel SCSI adapter or have the SCSI Host Adapter built into the motherboard. In either case, IBM’s SCSI interface uses a special 60-pin mini-Centronics type external shielded connector that is unique in the industry. A special IBM cable is required to adapt this connector to the standard 50-pin Centronics style connector used on most external SCSI devices. The pinout of the IBM 60-pin mini-Centronics style External Shielded connector is shown Table 2.7. Notice that although the pin arrangement is unique, the pin number to signal designations correspond with the standard unshielded internal pin header type of SCSI connector.

Table 2.7  IBM PS/2 SCSI External Shielded 60-Pin Connector.

Signal Name Pin Pin Signal Name

GROUND 1 60 Not Connected
-DB(0) 2 59 Not Connected
GROUND 3 58 Not Connected
-DB(1) 4 57 Not Connected
GROUND 5 56 Not Connected
-DB(2) 6 55 Not Connected
GROUND 7 54 Not Connected
-DB(3) 8 53 Not Connected
GROUND 9 52 Not Connected
-DB(4) 10 51 GROUND
GROUND 11 50 -I/O
-DB(5) 12 49 GROUND
GROUND 13 48 -REQ
-DB(6) 14 47 GROUND
GROUND 15 46 -C/D
-DB(7) 16 45 GROUND
GROUND 17 44 -SEL
-DB(Parity) 18 43 GROUND
GROUND 19 42 -MSG
GROUND 20 41 GROUND
GROUND 21 40 -RST
GROUND 22 39 GROUND
RESERVED 23 38 -ACK
RESERVED 24 37 GROUND
Open 25 36 -BSY
TERMPWR 26 35 GROUND
RESERVED 27 34 GROUND
RESERVED 28 33 GROUND
GROUND 29 32 -ATN
GROUND 30 31 GROUND

The P cable (Single-Ended) and connectors are used in 16-bit wide SCSI-2 applications (see table 2.8 for the pinout).

Table 2.8  P Cable (Single-Ended) Internal or External Shielded Connector.

Signal Name Pin Pin Signal Name

GROUND 1 35 -DB(12)
GROUND 2 36 -DB(13)
GROUND 3 37 -DB(14)
GROUND 4 38 -DB(15)
GROUND 5 39 -DB(Parity 1)
GROUND 6 40 -DB(0)
GROUND 7 41 -DB(1)
GROUND 8 42 -DB(2)
GROUND 9 43 -DB(3)
GROUND 10 44 -DB(4)
GROUND 11 45 -DB(5)
GROUND 12 46 -DB(6)
GROUND 13 47 -DB(7)
GROUND 14 48 -DB(Parity 0)
GROUND 15 49 GROUND
GROUND 16 50 GROUND
TERMPWR 17 51 TERMPWR
TERMPWR 18 52 TERMPWR
RESERVED 19 53 RESERVED
GROUND 20 54 GROUND
GROUND 21 55 -ATN
GROUND 22 56 GROUND
GROUND 23 57 -BSY
GROUND 24 58 -ACK
GROUND 25 59 -RST
GROUND 26 60 -MSG
GROUND 27 61 -SEL
GROUND 28 62 -C/D
GROUND 29 63 -REQ
GROUND 30 64 -I/O
GROUND 31 65 -DB(8)
GROUND 32 66 -DB(9)
GROUND 33 67 -DB(10)
GROUND 34 68 -DB(11)

The Q Cable (Single-Ended) and connector is defined only for 32-bit SCSI implementations, which also require a P able as well. 32-bit SCSI applications are rare to virtually nonexistent.

Differential SCSI

Differential SCSI is not normally used in a PC environment, but is very popular with minicomputer installations due to the very long bus lengths that are allowed.

The A cable (Differential) connector is available in both internal unshielded form as well as an external shielded form.

The P able (Differential) and Connector is used for 16-bit wide SCSI connections.

The Q cable (Differential) and connector is used only with the proposed 32-bit wide SCSI implementations (which have not been implemented by the marketplace as of yet), and in that case would also require a 16-bit wide P-cable.

Previous Table of Contents Next