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Parallel Pinout Diagrams

 
SCSI Pinouts

 

Speed:

Slow SCSI max 5Mbyte/s

 

Fast SCSI min 5Mbyte/s

Length:

Single-ended SCSI max 6m

 

Differential SCSI max 25m

Word length:

Narrow SCSI has 8-bit data transfer

 

Wide SCSI has 16- or 32-bit data transfers

 

An overview
 

 

SCSI

Speed (MBps)

Bus Width

Cable

Pins

ID's

Connector

SCSI-1

1 to 5

8

A

25 or 50

8

Sub-D25, Amphenol 50, Sub-D50

SCSI-2

5 to 10

8

A

50

8

Micro-D50

SCSI-2 fast/wide

up to 40

16

A&B

50

8

Micro-D50

SCSI-3

 

16

P

68

32

Micro-D68

SCSI-3 fast/wide

 

32

P&Q

68

32

Micro-D68

SCSI-4?

 

32

L

110

 

 

 

General
SCSI stands for Small Computer System Interface. The name is misleading, because SCSI is primirally used in the larger machines, (486, pentium, mini's and mainframes). The SCSI interface is a parallel interface, which means the data is not send one bit after another, but several bits over several lines at the same time. The communication between devices is done by initiators and targets. An initiator is a device which requests something from a target. The initiator is most commonly a host-adapter in a computer.
The target is the one that takes the job and carries it out. Because of the definition of SCSI that a job is given by a initiator and then carried out by a target without the initiator knowing how the target is doing it and even not knowing when the job is done the roles of initiator and target may switch. As soon as the target is done with it's job it initiats the host, which will become target.
The purpose of all this is that as soon as the target knows what the initiator wants the bus will become free for other jobs to be send to other targets. The bus is used more economically. Instead of a computer waiting for data coming from a scanner, the bus can be used by the computer to read data from the harddisk.
SCSI is not like other parallel buses like centronics. SCSI has the capability to connect more than two devices to a bus. These devices may be targets or initiators. So it is possible for two hosts to share one tapestreamer, but it is also possible for one host to have acces to several harddisks. The identification of the devices is done by an ID. SCSI-1 and SCSI-2 have a maximum of 8 ID's and SCSI-3 has even 32 possible ID's.There is no such thing as plain SCSI. There is SCSI-1, -2 and -3 and together with this there is Differential and Single-ended, and for the termination there is passive and active. Single-ended means that there is a ground and a signal wire. Much like in RS232. Differential on the other hand has no ground wire, but al signals have two wires, a positive and a negative one and the voltage difference between them carries the information (1 or 0). Much like RS422.
To make everything more complex the SCSI bus must be terminated to work properly, like in LAN networks. But LANs only use passive termination, which means a resistor is placed at the end and at the beginning of the cable, that's all. In SCSI there is also active termination, which means the termination is done by a voltage regulator and some resitors. This is for the Single-Ended interface. With differential SCSI live is easier. There is only passive termination. But it's not the same termination as for passive single-ended SCSI. And finally there is the difference between SCSI-3 and SCSI-2 wide. Both have 16 bytes transmissions, but SCSI-2 has only 50 wires and SCSI-3 has 68, so why take a, more expensive cable?
Due to the fact that SCSI-2 has a 50 wire cable and only 8 data lines there will be a low and high byte transmission. Each 16 bit word is split in a low and a high byte. These are transmitted one after the other and thus taking twice as long as 16 bit SCSI-3. This makes SCSI-3 faster and more economic.

Pinnings

Sub-D25 Male

Sub-D25 Female

Pin

Signal

Abbr.

Source

1

REQ

2

MSG

3

I/O

4

AST

5

ACK

6

BSY

7

GND

8

DB0

9

GND

10

DB3

11

DB5

12

DB6

13

DB7

14

GND

15

C/D

16

GND

17

ATN

18

GND

19

Select

SEL

20

DBP

21

DB1

22

DB2

23

DB4

24

GND

25

N/C

Found on Mac Plus/SE/II.
Termination power (TERMPWR) is not provided by the Macintosh. Special precaution is necessary when considering a SCSI device for this port. Check with the SCSI device manufacturer to make sure the device provides termination power.

Sub-D50 Male

Sub-D50 Female

Centronics 50 Female

Centronics 50 Male

Pin

Singel-Ended

Differential

1

GND

GND

2

GND

D0+

3

GND

D1+

4

GND

D2+

5

GND

D3+

6

GND

D4+

7

GND

D5+

8

GND

D6+

9

GND

D7+

10

GND

DPAR+

11

GND

DIFFSENS

12

Reserved

Reserved

13

Open

TERMPWR

14

Reserved

Reserved

15

GND

ATN+

16

GND

GND

17

GND

BSY+

18

GND

ACK+

19

GND

RST+

20

GND

MSG+

21

GND

SEL+

22

GND

C/D+

23

GND

REQ+

24

GND

I/O+

25

GND

GND

26

D0-

GND

27

D1-

D0-

28

D2-

D1-

29

D3-

D2-

30

D4-

D3-

31

D5-

D4-

32

D6-

D5-

33

D7-

D6-

34

DPAR-

D7-

35

GND

DPAR-

36

GND

GND

37

Reserved

Reserved

38

TRMPWR

TRMPWR

39

Reserved

Reserved

40

GND

GND

41

ATN-

ATN-

42

GND

GND

43

BSY-

BSY-

44

ACK-

ACK-

45

RST-

RST-

46

MSG-

MSG-

47

SEL-

SEL-

48

C/D-

C/D-

49

REQ-

REQ-

50

I/O-

I/O-

Micro-D50 Male

Micro-D50 Female

Pin

Singel-Ended

Differential

1

GND

GND

2

GND

D0+

3

GND

D1+

4

GND

D2+

5

GND

D3+

6

GND

D4+

7

GND

D5+

8

GND

D6+

9

GND

D7+

10

GND

DPAR+

11

GND

DIFFSENS

12

Reserved

Reserved

13

Open

TERMPWR

14

Reserved

Reserved

15

GND

ATN+

16

GND

GND

17

GND

BSY+

18

GND

ACK+

19

GND

RST+

20

GND

MSG+

21

GND

SEL+

22

GND

C/D+

23

GND

REQ+

24

GND

I/O+

25

GND

GND

26

D0-

GND

27

D1-

D0-

28

D2-

D1-

29

D3-

D2-

30

D4-

D3-

31

D5-

D4-

32

D6-

D5-

33

D7-

D6-

34

DPAR-

D7-

35

GND

DPAR-

36

GND

GND

37

Reserved

Reserved

38

TRMPWR

TRMPWR

39

Reserved

Reserved

40

GND

GND

41

ATN-

ATN-

42

GND

GND

43

BSY-

BSY-

44

ACK-

ACK-

45

RST-

RST-

46

MSG-

MSG-

47

SEL-

SEL-

48

C/D-

C/D-

49

REQ-

REQ-

50

I/O-

I/O-

Micro-D68 Male

Micro-D68 Female

Single-Ended

Pin

Signal

Pin

Signal

Pin

Signal

1

GND

24

GND

47

D7-

2

GND

25

GND

48

DPAR-

3

GND

26

GND

49

GND

4

GND

27

GND

50

GND

5

GND

28

GND

51

TRMPWR

6

GND

29

GND

52

TRMPWR

7

GND

30

GND

53

Reserved

8

GND

31

GND

54

GND

9

GND

32

GND

55

ATN-

10

GND

33

GND

56

GND

11

GND

34

GND

57

BSY-

12

GND

35

D12-

58

ACK-

13

GND

36

D13-

59

RST-

14

GND

37

D14-

60

MSG-

15

GND

38

D15-

61

SEL-

16

GND

39

DPAR-

62

C/D-

17

TRMPWR

40

D0-

63

REQ-

18

TRMPWR

41

D1-

64

I/O-

19

Reserved

42

D2-

65

D8-

20

GND

43

D3-

66

D9-

21

GND

44

D4-

67

D10-

22

GND

45

D5-

68

D11-

23

GND

46

D6-


 

Differential

PinSignalPinSignalPinSignal

1

D12+

24

RST+

47

D6-

2

D13+

25

MSG+

48

D7-

3

D14+

26

SEL+

49

DPAR-

4

D15+

27

C/D+

50

GND

5

DPARH+

28

REQ+

51

TRMPWR

6

GND

29

I/O+

52

TRMPWR

7

D0+

30

GND

53

Reserved

8

D1+

31

D8+

54

ATN-

9

D2+

32

D9+

55

GND

10

D3+

33

D10+

56

BSY-

11

D4+

34

D11+

57

ACK-

12

D5+

35

D12+

58

RST-

13

D6+

36

D13+

59

MSG-

14

D7+

37

D14+

60

SEL-

15

DPAR+

38

D15+

61

C/D-

16

DIFFSENS

39

DPARH+

62

REQ-

17

TRMPWR

40

GND

63

I/O-

18

TRMPWR

41

D0-

64

GND-

19

Reserved

42

D1-

65

D8-

20

ATN+

43

D2-

66

D9-

21

GND

44

D3-

67

D10-

22

BSY+

45

D4-

68

D11-

23

ACK+

46

D5-