[Coco] 8" drive to 5.25" replacement?

[Willard Goosey]

>From: Roger Taylor <rtaylor at bayou.com>
>Date: Tue, 02 Dec 2003 22:53:58 -0600

>I told them it might be best to try to replace the drive with an older 
>5.25" drive that can do single-density mode.  What I wanted to ask you guys 
>is if the cables are compatible between 8" and 5.25" drives.

Actually it's the newer (1.2M) HD 5.25" drives that can pretend to be 8"
drives.  That's the 500Kbit/second data rate, spinning the disk at 360
rpm, 80 tracks  (77 for 8", actually).  

The TEAC 55G was originally introduced as a drop-in replacement for 8"
drives.

I don't think the drive itself cares if it's writing/reading FM or MFM
data (single or double density)

They will need to build a cable converter.  8" drives normally use a
50-pin connector, and 5.25" drives use a 34-pin connector.  I have
one, but it's designed to go to a DD 5.25" drive, and they changed the
pinout slightly for HD drives.  

Here's the HD floppy PC pinout:
Floppy Disk Controller IDC-34 Male
pin     assignment      pin     assignment
1       GND             2       Density Select
3       GND             4       (reserved)
5       GND             6       (reserved)
7       GND             8       Index
9       GND             10      Motor Enable A
11      GND             12      Drive Sel B
13      GND             14      Drive Sel A
15      GND             16      Motor Enable B
17      GND             18      Direction
19      GND             20      Step
21      GND             22      Write Data
23      GND             24      Floppy Write Enable
25      GND             26      Track 0
27      GND             28      Write Protect
29      GND             30      Read Data
31      GND             32      Head Select
33      GND             34      Disk Change

I don't seem to have the 50-pin 8" drive pinout on-line... Shame on
me!  

Here's a pinout for going the other way, hooking a 8" drive to a PC.

34 pin (5.25")                                      50 pin (8")
2               Reduced Write                   >       NC
4               Not used                                NC
6               Drive Select "3"                >       32  DS3
8               Index                           <       20
10              Drive Select "0"                >       26  DS0
12              Drive Select "1" "B"            >       28  DS1
14              Drive Select "2" "A"            >       30  DS2
16              Motor On                        >       18  Head Load
18              Direction                       >       34
20              Step                            >       36
22              Write Data                      >       38
24              Write Gate                      >       40
26              Track 0                         <       42
28              Write Protect                   <       44
30              Read Data                       <       46
32              Side select                     >       14
34              Disk Change/Ready               <       22      Ready

All odd numbered wires are grounded.

I've never tried it, and I'm not sure if it would need to be changed
to go the other way...  You'd have to do something with line 2, which
became Density Select

There are other issues... check out
http://nemesis.lonestar.org/computers/tandy/hardware/model16_6000/floppyfix.html
for complete info.  

>
>thx
>
>{Roger Taylor}
>
Willard
-- 
Willard Goosey  goosey at sdc.org
Socorro, New Mexico, USA
"I've never been to Contempt!  Isn't that somewhere in New Mexico?"
   --- Yacko