IBM DBA-ESDI Hard Drives

DASD Storage Interface Specification Micro Channel (Rev. 2.2, Sep 1991)

Systems with DBA-ESDI
Direct Bus Attachment Pinout
Edge Connector Type
   Straight Connector
   Right Angle Connector
WD387 60MB Drive PCB

Systems with DBA-ESDI

A list of systems equipped with the DBA-ESDI interface:

Direct Bus Attachment Pinout

The following table shows the signal assignment and pin numbering for the 2 x 36-pin hard drive edge connector. Side A of the connector is the top (component side) and Side B is the bottom (solder side).

This is a subset of the standard Micro Channel slot (16-bit).

A02OA 13B02OA 14
A04OA 11B04OReserved / 14.3 MHz OSC 1)
A05OA 10B05Ground
A06OA 09B06OA 12
A07O+5 VdcB07O-CMD
A09OA 07B09Ground
A10OA 06B10I/OD 01
A11GroundB11I/OD 03
A12OA 05B12I/OD 04
A13OA 04B13Ground
A15O+5 VdcB15I/OD 08
A16OA 02B16I/OD 09
A17OA 01B17Ground
A18OA 00B18I/OD 12
A19O+12 VdcB19I/OD 14
A20O-ADLB20I/OD 15
A23O+5 VdcB23I/OD 02
A24IARB 00B24I/OD 05
A25IARB 01B25Ground
A26IARB 02B26I/OD 06
A27+12 VdcB27I/OD 07
A28IARB 03B28I/OD 10
A30O–TCB30I/OD 11
A31+5 VdcB31I/OD 13
A34OM/-IOB34I-CD DS 16
A35GroundB35I-IRQ 14

1) The signal is marked as 14.3 MHz OSC in the Model 70 technical reference and as "Reserved" in the P70 and 55 SX reference. It's not confirmed whether the signal exists in all implementations.

There is a physical key between pins 2 and 3 (A02 and A03; B02 and B03). Not all connectors have the key present.


Edge Connector Type

2x36-pin card edge connector, 2.54mm (0.100") pin pitch.
Through-hole; straight or right angle type.

Straight Connector

Used on the Model 50 HDD adapters, the Model 70 drive riser, as well as some PS/55 machines.

AMP 650076-1

No datasheet found so far.

Right Angle Connector

Used on the Model 90 planar (early samples only). The Japanese 5560 planar also has a provision for a pair of these connectors.

Thomas & Betts HOLMBERG A8D36RA 29C

Thomas & Betts 1992 Full-Line Catalog (physical page 191 onwards)

A8 - Series Designator; A8 - 600 V DC
D36 - Number of contact pairs and readout; D - Double Readout, 36 - # contact pairs
RA - Termination style; Right angle dip solder tails
29 - Contact plating; 29 - Standard Plating (see datasheet for details)
C - Mounting style; C - Without mounting ears

Hirose Electronics A810056101

No datasheet found so far.

WD387 60MB PCB

D15 Activity LED
J4 7x2-pin header (2 keys)
J7 2-pin header
J2 20-pin header
U3 SSI 32P541-CH Read Data Processor
U5 S80C31-1 MCU
U7 K1-230 microcode ROM?
U8 Hitachi HD64950CPB Hard Disk Ctrl.
U17 HM6264ALFP-15T
U9 TC8564AF
U11 TC17G032AF 6127911
U15 P/N 6127914
Y1 16KSS0A
Y3 3.6DKSS0B

160MB DBA-ESDI PCB 79F6370

There are no reference designators silkscreened on the PCB.

S80C196KB12 MCU
Hitachi 65256BLFP-10T
M5M5256BFP-70L 32Kx8 SRAM
32D535-CW Sync/RLL ENDEC
79F6265 ROM? (SOIC-28)
TA7736P Motor Driver
32P541-CH Read Data Processor
38F7621 / M52831FP
D240B1 osc

Modifying 160MB SCSI Drive With ESDI PCB

Modifying a 160 MB SCSI Disk was only half way successful (took of the SCSI PCB and hooked up the ESDI PCB from my bad 120 MB Drive). I can see the HD when booting with the Refdisk, but I get all kinds of errors when trying to format it.

The 160 operates with a different number of sectors IIRC. Only have the data for the 80 and 160MB: 984 cylinders, 10 heads, 17 (80) and 34 (160) sectors. So the 120 must have 26 sectors (25.5 arithmetically - but there are no half cylinders ...). I think the 120MB controller cannot "fetch" a valid sector start ... and therefore jumps out. The LLFORMAT routine does not go *that* deep that it can write raw sectors on the media. That's usually the purpose of some factory tools.

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