SCSI (Small Computer System Interface)
This document describe SCSI parallel connectors.
Some information are from Bernard-Yves Cochain SCSI Web site (in french).

Interface information
Bus width

WidthExternal connectorInternal connector
Narrow
(8bit)
DB25
LD50
HD50
HE50
Wide
(16bit)
2*HD50
HD68
HD68
SCA80
Wide32
(32bit)
2*HD68
2*HD68
Note: There are also serial SCSI connectors - IEEE-1394 and SAS (Serial Attached SCSI).

Adaptec decided to associate a color with each external SCSI connector, here is a list of these :
External connectorAdaptec Color Code
DB 25-pin White
HD 50-pin Orange
HD 68-pin Red
Note: I suppose there is also a color for Centronics 50-pin.

Bus Speed

SpeedFrequencyNarrow speedWide speed
SCSI? 5MHz1,5 to 5 MB/s/ [no wide device]
Fast SCSI10MHz10 MB/s20 MB/s
Ultra SCSI20MHz20 MB/s40 MB/s
Ultra2 SCSI40MHz40 MB/s80 MB/s
Ultra 160/m? 80MHz/ [no narrow device]160 MB/s
Note: "Ultra 160/m" is not a SCSI standard yet, it's Adaptec version of the upcoming Ultra3 standard.

Narrow

DB25 (Apple) Connector

Apple decided to use a DB25 connector for SCSI (narrow), but this doesn't allow twisted pairs and is not complient to SCSI standards.
Some companies like Iomega still use this connector on new devices besides they can cause many troubles on SCSI busses using faster devices such as UltraSCSI (Iomega itself doesn't recommand using more than one DB25 device, but still use it for Zip drives).
This connector should not be used anymore for new design, use HD50 instead.


DescriptionNamePin PinNameDescription
RequestREQ1 14GNDGround
MessageMSG2 15C/DCommand/-Data
Input/OutputI/O3 16GNDGround
ResetRST4 17ATNAttention
AcknowledgeACK5 18GNDGround
BusyBSY6 19SELSelection
GroundGND7 20DPData parity bit
Data bit 0D08 21D1Data bit 1
GroundGND9 22D2Data bit 2
Data bit 3D310 23D4Data bit 4
Data bit 5D511 24GNDGround
Data bit 6D612 25TermPwrTermination power
Data bit 7D713  

Narrow external (LD50 & HD50)

LD50 and HD50 use the same pinout, so this table apply to both of them.

LD50 is SCSI-1 standard and is still used for many narrow (formerly called 8bit SCSI) devices. Consider using the HD50 for new designs.
HD50 is SCSI-2 standard, fully compatible with LD50, support higher frequency such as UltraSCSI and is smaller.
DescriptionNamePin PinNameDescription
Twisted pair GroundGND1 26D0Data bit 0
Twisted pair GroundGND2 27D1Data bit 1
Twisted pair GroundGND3 28D2Data bit 2
Twisted pair GroundGND4 29D3Data bit 3
Twisted pair GroundGND5 30D4Data bit 4
Twisted pair GroundGND6 31D5Data bit 5
Twisted pair GroundGND7 32D6Data bit 6
Twisted pair GroundGND8 33D7Data bit 7
Twisted pair GroundGND9 34DPData Parity bit
GroundGND10 35GNDGround
GroundGND11 36GNDGround
Reserved 12 37 Reserved
  13 38TermPwrTermination Power (+5V)
Reserved 14 39 Reserved
GroundGND15 40GNDGround
Twisted pair GroundGND16 41ATNAttention
GroundGND17 42GNDGround
Twisted pair GroundGND18 43BSYBusy
Twisted pair GroundGND19 44ACKAcknowledge
Twisted pair GroundGND20 45RSTReset
Twisted pair GroundGND21 46MSGMessage
Twisted pair GroundGND22 47SELSelection
Twisted pair GroundGND23 48C/DCommand/-Data
Twisted pair GroundGND24 49REQRequest
Twisted pair GroundGND25 50I/OInput/Output
Note: signals positions are the same as on HE50 internal narrow connector, only pin numbers are different because of the connectors differences.

Narrow internal (HE50)

Internal Narrow SCSI cable, similar to external LD50 and HD50.


DescriptionNamePin PinNameDescription
Twisted pair GroundGND1 2D0Data bit 0
Twisted pair GroundGND3 4D1Data bit 1
Twisted pair GroundGND5 6D2Data bit 2
Twisted pair GroundGND7 8D3Data bit 3
Twisted pair GroundGND9 10D4Data bit 4
Twisted pair GroundGND11 12D5Data bit 5
Twisted pair GroundGND13 14D6Data bit 6
Twisted pair GroundGND15 16D7Data bit 7
Twisted pair GroundGND17 18DPData Parity bit
GroundGND19 20GNDGround
GroundGND21 22GNDGround
Reserved 23 24 Reserved
  25 26TermPwrTermination Power (+5V)
Reserved 27 28 Reserved
GroundGND29 30GNDGround
Twisted pair GroundGND31 32ATNAttention
GroundGND33 34GNDGround
Twisted pair GroundGND35 36BSYBusy
Twisted pair GroundGND37 38ACKAcknowledge
Twisted pair GroundGND39 40RSTReset
Twisted pair GroundGND41 42MSGMessage
Twisted pair GroundGND43 44SELSelection
Twisted pair GroundGND45 46C/DCommand/-Data
Twisted pair GroundGND47 48REQRequest
Twisted pair GroundGND49 50I/OInput/Output
Note: signals positions are the same as on HD50 and LD50 connectors, only pin numbers are different because of the connectors differences.

Wide

Wide external (HD68)

This connector is used for external Wide devices.
For 8bit devices, the HD50 should be used instead.


DescriptionNamePin PinNameDescription
Twisted pair GroundGND1 35D12Data bit 12
Twisted pair GroundGND2 36D13Data bit 13
Twisted pair GroundGND3 37D14Data bit 14
Twisted pair GroundGND4 38D15Data bit 15
Twisted pair GroundGND5 39DP1Data Parity bit 1
Twisted pair GroundGND6 40D0Data bit 0
Twisted pair GroundGND7 41D1Data bit 1
Twisted pair GroundGND8 42D2Data bit 2
Twisted pair GroundGND9 43D3Data bit 3
Twisted pair GroundGND10 44D4Data bit 4
Twisted pair GroundGND11 45D5Data bit 5
Twisted pair GroundGND12 46D6Data bit 6
Twisted pair GroundGND13 47D7Data bit 7
Twisted pair GroundGND14 48DP0Data Parity bit 0
GroundGND15 49GNDGround
GroundGND16 50GNDGround
Termination Power (+5V)TermPwr17 51TermPwrTermination Power (+5V)
Termination Power (+5V)TermPwr18 52TermPwrTermination Power (+5V)
Reserved 19 53 Reserved
GroundGND20 54GNDGround
Twisted pair GroundGND21 55ATNAttention
GroundGND22 56GNDGround
Twisted pair GroundGND23 57BSYBusy
Twisted pair GroundGND24 58ACKAcknowledge
Twisted pair GroundGND25 59RSTReset
Twisted pair GroundGND26 60MSGMessage
Twisted pair GroundGND27 61SELSelection
Twisted pair GroundGND28 62C/DCommand/-Data
Twisted pair GroundGND29 63REQRequest
Twisted pair GroundGND30 64I/OInput/Output
Twisted pair GroundGND31 65D8Data bit 8
Twisted pair GroundGND32 66D9Data bit 9
Twisted pair GroundGND33 67D10Data bit 10
Twisted pair GroundGND34 68D11Data bit 11

Wide internal (HD68)

This connector is used for internal Wide devices, for 8bit devices, the HE50 should be used instead.


Documentation not available yet.

Wide32

Wide32 external (Dual HD68)

P
DescriptionNamePin PinNameDescription
Twisted pair GroundGND1 35D12Data bit 12
Twisted pair GroundGND2 36D13Data bit 13
Twisted pair GroundGND3 37D14Data bit 14
Twisted pair GroundGND4 38D15Data bit 15
Twisted pair GroundGND5 39DP1Data Parity bit 1
Twisted pair GroundGND6 40D0Data bit 0
Twisted pair GroundGND7 41D1Data bit 1
Twisted pair GroundGND8 42D2Data bit 2
Twisted pair GroundGND9 43D3Data bit 3
Twisted pair GroundGND10 44D4Data bit 4
Twisted pair GroundGND11 45D5Data bit 5
Twisted pair GroundGND12 46D6Data bit 6
Twisted pair GroundGND13 47D7Data bit 7
Twisted pair GroundGND14 48DP0Data Parity bit 0
GroundGND15 49GNDGround
GroundGND16 50GNDGround
Termination Power (+5V)TermPwr17 51TermPwrTermination Power (+5V)
Termination Power (+5V)TermPwr18 52TermPwrTermination Power (+5V)
Reserved 19 53 Reserved
GroundGND20 54GNDGround
Twisted pair GroundGND21 55ATNAttention
GroundGND22 56GNDGround
Twisted pair GroundGND23 57BSYBusy
Twisted pair GroundGND24 58ACKAcknowledge
Twisted pair GroundGND25 59RSTReset
Twisted pair GroundGND26 60MSGMessage
Twisted pair GroundGND27 61SELSelection
Twisted pair GroundGND28 62C/DCommand/-Data
Twisted pair GroundGND29 63REQRequest
Twisted pair GroundGND30 64I/OInput/Output
Twisted pair GroundGND31 65D8Data bit 8
Twisted pair GroundGND32 66D9Data bit 9
Twisted pair GroundGND33 67D10Data bit 10
Twisted pair GroundGND34 68D11Data bit 11
Q
DescriptionNamePin PinNameDescription
Q cable not available yet.
Note: P connector is a standard Wide external connector.

CONNETTORE SCSI a 68PIN

Piedino

Segnale

Piedino

Segnale

1 Messa a terra 35 Dati 12
2 Messa a terra 36 Dati 13
3 Messa a terra 37 Dati 14
4 Messa a terra 38 Dati 15
5 Messa a terra 39 Dati P1
6 Messa a terra 40 Dati 0
7 Messa a terra 41 Dati 1
8 Messa a terra 42 Dati 2
9 Messa a terra 43 Dati 3
10 Messa a terra 44 Dati 4
11 Messa a terra 45 Dati 5
12 Messa a terra 46 Dati 6
13 Messa a terra 47 Dati 7
14 Messa a terra 48 Dati P0
15 Messa a terra 49 Riservato
16 Messa a terra 50 Messa a terra
17 Alimentazione terminale 51 Alimentazione terminale
18 Alimentazione terminale 52 Alimentazione terminale
19 Riservato 53 Riservato
20 Messa a terra 54 Messa a terra
21 Messa a terra 55 - Attenzione
22 Messa a terra 56 Messa a terra
23 Messa a terra 57 - Occupato
24 Messa a terra 58 - Riconoscimento
25 Non collegato 59 - Reimpostazione
26 Messa a terra 60 - Messaggio
27 Messa a terra 61 - Selezione
28 Messa a terra 62 - Controllo/Dati
29 Messa a terra 63 - Richiesta
30 Messa a terra 64 -Immissione/Emissione
31 Messa a terra 65 Dati 8
32 Messa a terra 66 Dati 9
33 Messa a terra 67 Dati 10
34 Messa a terra 68 Dati 11