 |
Parallel SCSI connectors
Physical connectors
| Connector |
SCSI standards |
Notes |
DB25 - external |
Apple narrow SCSI |
Legacy SCSI interface designed by those lunatics in California. Doesn't adhere to any sane standard, doesn't allow the use of twisted pairs for the data conductors and hence the only other people to use it are Iomega and the occasional scanner manufacturer :-) Avoid wherever possible! |
Centronics 50 - external |
SCSI 1 external |
Proper chunky connector resembling a parallel printer connector with a few more pins. Flat out, this monster can shift a whopping 5MB every second! WOW! |
DB50-HD - external |
SCSI 2 external |
This connector allows for 10MB/sec SCSI-2 and is generally found on things like Iomega Jaz drives, external DDS streamers etc. |
HE50 - internal |
SCSI 1/2 internal |
Insulation displacement connector for 50-way internal ribbon connectors. Fairly robust, but an absolute bastard to remove without damaging the ribbon when they've been seated for a while... |
DB68-HD - internal / external |
(Ultra / Ultra160 / Ultra 320)Wide SCSI |
68-pin connector that finds itself on the rear face of plenty of drive arrays. This is a current connector and handles all the way up to the latest Ultra-320 spec. |
SCA-80 - internal |
(Ultra / Ultra160 / Ultra 320)Wide SCSI |
Midi-centronics connector that carries both SCSI data and power to an individual drive. Used to allow hot-swapping of SCSI drives in systems that support it. The drives are usually semi-enclosed by a 'sled' that guides the connector accurately into a matching SCA backplane. Note that, unless you really know what you're doing, 'hotplugging drives' is usually a synonym for 'breaking stuff in a horribly expensive manner'. |
Bus speeds
| Speed |
Frequency |
Narrow (8-bit) speed |
Wide (16-bit) speed |
| SCSI |
5MHz |
1.5 to 5 MB/s |
[no wide device] |
| Fast SCSI |
10MHz |
10MB/s |
20MB/s |
| Ultra SCSI |
20MHz |
20MB/s |
40MB/s |
| Ultra2 SCSI |
40MHz |
40MB/s |
80MB/s |
| Ultra 160 |
80MHz |
[no narrow device] |
160MB/s |
| Ultra 320 |
80MHz with clever sideband addressing |
[no narrow device] |
320MB/s |
SCSI connector pinouts
DB25 (Apple) Connector
As mentioned above, Apple decided to use a DB25 connector for narrow SCSI on the earlier Macs, but this doesn't allow twisted data pairs in the cable (bad idea) and as such is not complient to SCSI standards. Daisychaining DB25 devices is not the best idea in the world and a cable longer than 75cm seems to introduce so many errors it's simply not worth bothering with. This interconnection format should have been put to bed a long time ago!
| Description |
Name |
Pin |
|
Pin |
Name |
Description |
| Request | REQ | 1 | 14 | GND | Ground |
| Message | MSG | 2 | 15 | C/D | Command/-Data |
| Input/Output | I/O | 3 | 16 | GND | Ground |
| Reset | RST | 4 | 17 | ATN | Attention |
| Acknowledge | ACK | 5 | 18 | GND | Ground |
| Busy | BSY | 6 | 19 | SEL | Selection |
| Ground | GND | 7 | 20 | DP | Data parity bit |
| Data bit 0 | D0 | 8 | 21 | D1 | Data bit 1 |
| Ground | GND | 9 | 22 | D2 | Data bit 2 |
| Data bit 3 | D3 | 10 | 23 | D4 | Data bit 4 |
| Data bit 5 | D5 | 11 | 24 | GND | Ground |
| Data bit 6 | D6 | 12 | 25 | TermPwr | Termination power |
| Data bit 7 | D7 | 13 | |
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. |
| Description | Name | Pin | | Pin | Name | Description |
|---|
| Twisted pair Ground | GND | 1 |
26 | D0 | Data bit 0 |
| Twisted pair Ground | GND | 2 |
27 | D1 | Data bit 1 |
| Twisted pair Ground | GND | 3 |
28 | D2 | Data bit 2 |
| Twisted pair Ground | GND | 4 |
29 | D3 | Data bit 3 |
| Twisted pair Ground | GND | 5 |
30 | D4 | Data bit 4 |
| Twisted pair Ground | GND | 6 |
31 | D5 | Data bit 5 |
| Twisted pair Ground | GND | 7 |
32 | D6 | Data bit 6 |
| Twisted pair Ground | GND | 8 |
33 | D7 | Data bit 7 |
| Twisted pair Ground | GND | 9 |
34 | DP | Data Parity bit |
| Ground | GND | 10 |
35 | GND | Ground |
| Ground | GND | 11 |
36 | GND | Ground |
| Reserved | | 12 |
37 | | Reserved |
| | | 13 |
38 | TermPwr | Termination Power (+5V) |
| Reserved | | 14 |
39 | | Reserved |
| Ground | GND | 15 |
40 | GND | Ground |
| Twisted pair Ground | GND | 16 |
41 | ATN | Attention |
| Ground | GND | 17 |
42 | GND | Ground |
| Twisted pair Ground | GND | 18 |
43 | BSY | Busy |
| Twisted pair Ground | GND | 19 |
44 | ACK | Acknowledge |
| Twisted pair Ground | GND | 20 |
45 | RST | Reset |
| Twisted pair Ground | GND | 21 |
46 | MSG | Message |
| Twisted pair Ground | GND | 22 |
47 | SEL | Selection |
| Twisted pair Ground | GND | 23 |
48 | C/D | Command/-Data |
| Twisted pair Ground | GND | 24 |
49 | REQ | Request |
| Twisted pair Ground | GND | 25 |
50 | I/O | Input/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.
| Description | Name | Pin | | Pin | Name | Description |
|---|
| Twisted pair Ground | GND | 1 |
2 | D0 | Data bit 0 |
| Twisted pair Ground | GND | 3 |
4 | D1 | Data bit 1 |
| Twisted pair Ground | GND | 5 |
6 | D2 | Data bit 2 |
| Twisted pair Ground | GND | 7 |
8 | D3 | Data bit 3 |
| Twisted pair Ground | GND | 9 |
10 | D4 | Data bit 4 |
| Twisted pair Ground | GND | 11 |
12 | D5 | Data bit 5 |
| Twisted pair Ground | GND | 13 |
14 | D6 | Data bit 6 |
| Twisted pair Ground | GND | 15 |
16 | D7 | Data bit 7 |
| Twisted pair Ground | GND | 17 |
18 | DP | Data Parity bit |
| Ground | GND | 19 |
20 | GND | Ground |
| Ground | GND | 21 |
22 | GND | Ground |
| Reserved | | 23 |
24 | | Reserved |
| | | 25 |
26 | TermPwr | Termination Power (+5V) |
| Reserved | | 27 |
28 | | Reserved |
| Ground | GND | 29 |
30 | GND | Ground |
| Twisted pair Ground | GND | 31 |
32 | ATN | Attention |
| Ground | GND | 33 |
34 | GND | Ground |
| Twisted pair Ground | GND | 35 |
36 | BSY | Busy |
| Twisted pair Ground | GND | 37 |
38 | ACK | Acknowledge |
| Twisted pair Ground | GND | 39 |
40 | RST | Reset |
| Twisted pair Ground | GND | 41 |
42 | MSG | Message |
| Twisted pair Ground | GND | 43 |
44 | SEL | Selection |
| Twisted pair Ground | GND | 45 |
46 | C/D | Command/-Data |
| Twisted pair Ground | GND | 47 |
48 | REQ | Request |
| Twisted pair Ground | GND | 49 |
50 | I/O | Input/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.
| Description | Name | Pin | | Pin | Name | Description |
|---|
| Twisted pair Ground | GND | 1 |
35 | D12 | Data bit 12 |
| Twisted pair Ground | GND | 2 |
36 | D13 | Data bit 13 |
| Twisted pair Ground | GND | 3 |
37 | D14 | Data bit 14 |
| Twisted pair Ground | GND | 4 |
38 | D15 | Data bit 15 |
| Twisted pair Ground | GND | 5 |
39 | DP1 | Data Parity bit 1 |
| Twisted pair Ground | GND | 6 |
40 | D0 | Data bit 0 |
| Twisted pair Ground | GND | 7 |
41 | D1 | Data bit 1 |
| Twisted pair Ground | GND | 8 |
42 | D2 | Data bit 2 |
| Twisted pair Ground | GND | 9 |
43 | D3 | Data bit 3 |
| Twisted pair Ground | GND | 10 |
44 | D4 | Data bit 4 |
| Twisted pair Ground | GND | 11 |
45 | D5 | Data bit 5 |
| Twisted pair Ground | GND | 12 |
46 | D6 | Data bit 6 |
| Twisted pair Ground | GND | 13 |
47 | D7 | Data bit 7 |
| Twisted pair Ground | GND | 14 |
48 | DP0 | Data Parity bit 0 |
| Ground | GND | 15 |
49 | GND | Ground |
| Ground | GND | 16 |
50 | GND | Ground |
| Termination Power (+5V) | TermPwr | 17 |
51 | TermPwr | Termination Power (+5V) |
| Termination Power (+5V) | TermPwr | 18 |
52 | TermPwr | Termination Power (+5V) |
| Reserved | | 19 |
53 | | Reserved |
| Ground | GND | 20 |
54 | GND | Ground |
| Twisted pair Ground | GND | 21 |
55 | ATN | Attention |
| Ground | GND | 22 |
56 | GND | Ground |
| Twisted pair Ground | GND | 23 |
57 | BSY | Busy |
| Twisted pair Ground | GND | 24 |
58 | ACK | Acknowledge |
| Twisted pair Ground | GND | 25 |
59 | RST | Reset |
| Twisted pair Ground | GND | 26 |
60 | MSG | Message |
| Twisted pair Ground | GND | 27 |
61 | SEL | Selection |
| Twisted pair Ground | GND | 28 |
62 | C/D | Command/-Data |
| Twisted pair Ground | GND | 29 |
63 | REQ | Request |
| Twisted pair Ground | GND | 30 |
64 | I/O | Input/Output |
| Twisted pair Ground | GND | 31 |
65 | D8 | Data bit 8 |
| Twisted pair Ground | GND | 32 |
66 | D9 | Data bit 9 |
| Twisted pair Ground | GND | 33 |
67 | D10 | Data bit 10 |
| Twisted pair Ground | GND | 34 |
68 | D11 | Data 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.
This page was last updated: 30th September 2004 at 2:06pm BST
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