Drives

Floppy interface
IDE/ATA (Integrated Drive Electronics) interface
SCSI (Small Computer System Interface)

Floppy interface Back to top

The floppy disk interface support two 5¼ or 3½ drives (and a tape device or a 3rd floppy in some special cases).
Most new drives doesn't have jumpers for A or B setting, they are designed to be B drive only.
The cable is twisted at pins 9 to 16 which swap "Motor Enable A" and "Drive Select A" with "Motor Enable B" and "Drive Select B" signals, so the drive connected after the change receive signals for the A drive instead of signals for the B one.
I do not know how they use the 3rd device, I guess it could be something like using "Drive Select A" and "Drive Select B" signals at the same time.

Pins layout

Connector : HE34 (or Edge34 for old devices like 5¼ floppies)

IDE/ATA (Integrated Drive Electronics) interface Back to top

Pins layout

Connector : HE40

Note : When IDE have a DMA Request, it is usually the DMA3.

SCSI (Small Computer System Interface) Back to top

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

Interface information

Bus width

Width	External connector	Internal connector	SCA
Narrow (8bit)	DB25 LD50 HD50	HE50	/
Wide (16bit)	2*HD50 HD68	HD68	SCA80 [no picture yet]
Wide32 (32bit)	2*HD68	2*HD68	/

Note: There are also Serial SCSI Interfaces, IEEE-1394.

Adaptec decided to associate a color with each external SCSI connector, here is a list of these :

External connector		Adaptec 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

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.

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.

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.

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.

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)

Note: P connector is a standard Wide external connector.

Back to top