High
Resolution Photo (67k JPG)High
Resolution Photo (67k JPG)
The SWTPC 6800 and 6809 computer floppy disk controllers can use current production 3.5 inch drives without modification. While the drives support double-sided 80 track high-density operation they also work as a single-sided 35 track single-density drive. SWTPC FLEX for the 6809 already supports double-sided 80 track operation (and double density if your controller handles it.) SWTPC FLEX for the 6800 requires a simple modification to the NEWDISK routine to handle double-sided 80 track operation.
The only issue with current production 3.5 inch drives is that they are hard wired to Drive Select 1 (DS1 pin 12). You will needed to build a ribbon cable that swaps Drive Select 1 with Drive Select 0 (DS0 pin 10) to have a dual drive system. You can add a third drive by swapping Drive Select 1 with Drive Select 3 (DS3 pin 14.) The standard IBM PC ribbon cable swaps the motor-on control (pin 16) in addition to the drive select so they cannot be used on a stock SWTPC floppy controller. (My DC5 floppy controller supports PC cables.)
Most 3.5 inch drives have a "feature" that makes
them not work with a SWTPC DC-3 or DC-4 in the "09"
jumper setting for the Ready line. These drives require the Ready
jumper to be in the "00" position. The Index Pulse (pin
8) is "Masked" by a Seek Complete signal. In other words
the Index Pulse signal is off during a Seek. (So is the Read Data.)
Some of the older models had a jumper to control this but current
production drives have no jumpers. Current production drives that
mask the Index Pulse during Seek operations will not work the
stock SWTPC drivers in the "09" position. They work
fine in the "00" position but you give up the disk missing
from drive detection.
You can start with about 4 feet of 34 conductor ribbon cable and three 34 pin IDC sockets or a existing PC cable. The floppy controller end has no modifications. The floppy drive end need a twist in the ribbon for the drive 0 socket. To make the cable you need to separate conductors 10, 11 and 12 from the rest for the ribbon cable. Twist the conductors so that conductor 10 and 12 are swapped and install the socket.
You may also want to have a 34 pin card edge connector so you can use 5.25 inch drives. If you use a standard PC cable with a 5.25 inch drive that has a jumper for drive select 0 you can put a 3.5 inch drive on the same cable as drive 1. You can use this cable to boot from the 5.25 inch disk and then copy to the 3.5 inch disks.
High
Resolution Photo (91k JPG)
You will also need a power supply to run the drives. A 3.5 inch drive uses 5 volts at 1 amp peak while seeking . The drive does not use 12 volts. You can run two drives off a good 1 amp supply because only one drive is seeking at a time. The power supply show is a 2 amp switching supply that is only a few dollars more than a 1 amp unit. (Do not try to use the SWTPC 6800 for the 5 volt supply, it don't have any power to spare.)
You need to make an adapter from the power supply to a floppy disk style connector. Since wall mount power supplies have the center conductor positive and some negative I chose to permanently mount the floppy drive power connector to the supply. (I did not want to plug in the wrong power supply and blow up my whole system.) I cut a 5 inch drive power splitter in half to get the connector.
The two drives are held together with duct tape.
| Description | Part Number | Vendor | Order Number | Each | Qty | Cost |
| 3.5 Inch Floppy Drive | Teac FD235HF | na | na |
11.95 |
2 |
23.90 |
| 34 conductor gray ribbon cable | 171-34 | JAMECO | 37840 |
0.42 |
10 |
4.20 |
| 34 conductor idc socket, non-polarized | SN34 | JAMECO | 138341 |
0.35 |
2 |
0.70 |
| 34 conductor idc socket, polarized | S34 | JAMECO | 32643 |
0.45 |
1 |
0.45 |
| Regulated Power Supply 5V 2A | EPA101MU05 | JAMECO | 189190 |
9.95 |
1 |
9.95 |
| Power Splitter, 3.5 Inch Drive | PCY3 | JAMECO | 72303 |
2.49 |
1 |
2.49 |
| Power Splitter, 5 Inch Drive | PCY | JAMECO | 28353 |
2.75 |
1 |
2.75 |
| IDC Crimping Tool* | HT214 | JAMECO | 73251 |
11.95 |
0 |
0.00 |
| *optional | Total |
44.44 |
All of the parts can be purchased at www.jameco.com including the floppy drives. You can find better prices on floppy drives at computer stores. My local computer store has them for $12 or less.
Michael Holley's
SWTPC Collection Home Page
This page was last edited
March 02, 2015