StephensDev

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External Floppy Adapter

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Index

• Problem
• Build
• Sourcing Parts
• Configuration
• Final Results

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Problem

Like many IBM P70 models in circulation, mine also suffered from floppy drive issues. Despite my initial attempt at fixing it failing, I replaced it with a Gotek drive to keep my system functional. However, I found myself in a predicament—I wanted the flexibility to use both physical floppy disks and emulated ones with this device. Having just one floppy drive wasn't going to cut it for me.

After conducting some thorough research, I stumbled upon a potential solution. The external storage device port (HDI-30) on the IBM Personal System/2 5.25" external diskette drive (4869-001) caught my attention. It boasted compatibility with 360kb floppies, and upon consulting the IBM P70 technical reference, I discovered that the external storage device port contained all the necessary signals of a standard floppy drive.

So, why not bridge the gap with a HDI-30 to a 34-pin floppy adapter?

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Sourcing Parts

• HDI-30 Connector
• IDE 35 Pin Floppy Connector (or make your own like I did with a small prototype board and header pins)

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Build

• Open the Apple HDI-30 to SCSI Adapter.

• Desolder the SCSI connector.
• Solder wires based on the following diagram.

34 Pin Floppy Connector

Pin	I/O	Signal	Pin	I/O	Signal
1	I	2nd Drive Installed	2	O	High Density Select
3	O	+ 5 Vdc	4	N/A	Reserved
5	N/A	Ground	6	O	+ 12 Vdc
7	N/A	Ground	8	I	Index
9	N/A	Ground	10	N/A	Reserved
11	N/A	Ground	12	O	Drive Select
13	N/A	Ground	14	N/A	Reserved
15	N/A	Ground	16	O	Motor Enable
17	N/A	Ground	18	O	Direction
19	N/A	Ground	20	O	Step
21	N/A	Ground	22	O	Write Data
23	N/A	Ground	24	O	Write Enable
25	N/A	Ground	26	I	Track 0
27	N/A	Ground	28	I	Write Protect
29	N/A	Ground	30	I	Read Data
31	N/A	Ground	32	O	Side 1 Select
33	N/A	Ground	34	I	Diskette Change

HDI-30 Connector - Female

Pin	I/O	Signal	Pin	I/O	Signal
1	N/A	Ground	2	I	2nd Drive Installed
3	N/A	Ground	4	O	High Density Select
5	N/A	Ground	6	N/A	Reserved
7	N/A	Ground	8	I	Index
9	O	Motor Enable	10	O	Drive Select
11	N/A	Reserved	12	N/A	Reserved
13	N/A	Ground	14	O	Direction
15	N/A	Ground	16	O	Step
17	N/A	Ground	18	O	Write Data
19	N/A	Ground	20	O	Write Enable
21	N/A	Ground	22	I	Track 0
23	N/A	Ground	24	I	Write Protect
25	N/A	Ground	26	I	Read Data
27	N/A	Ground	28	O	Side 1 Select
29	N/A	Ground	30	I	Diskette Change

Signal Mapping.

HDI-30	In/out	Desc	Floppy Connector
2	I	2nd Drive Installed	1
4	O	High Density Select	2
8	I	Index	8
10	O	Drive Select	12
14	O	Direction	18
16	O	Step	20
18	O	Write Data	22
20	O	Write Enable	24
22	I	Track 0	26
24	I	Write Protect	28
26	I	Read Data	30
28	O	Side 1 Select	32
30	I	Diskette Change	34
9	O	Motor Enable	16

• Use the chart to map the pins and connect all ground wires together.
• Squeeze everything back into the case.
• Connect a straight (no twist) floppy cable between the adapter and your floppy drive (external power is needed).

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Configuration

Load your reference disk and set the second floppy drive to 1.44mb.

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Final Results

I am able to reference the b drive from dos 6.22.

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