TAGLANCE@ucs.UWPLATT.EDU (LANCE TAGLIAPIETRA) (04/14/91)
[NOTE: The following was originally posted on the BitNet list COCO@PUCC - Tandy Color Computer discussion. Given the recent discussion on floppy disk systems, this might be usefull to others on this discussion -- Lance] Adding 3.5 inch Drives These drive, as sold by most vendors, use 80 tracks, double-sided, and store 720 Kbytes of data. They are electrically the same as a 5 1/4 inch floppy drives and can easily be added using the 80 track drives that have been included with OS9 Level II. Also, several companies are selling adapter kits to allow you to install these in a 5 1/4 inch drive enclosure. This is the best way to go, but -- like me, many users will prefer to install them as an addition to their current system instead of a replacement. DRIVERS ------- As I said above, any of the drivers that are included with Level II can be used as long as the 80 track descriptors are included in your bootfile for the new disk drive. Microware has thougtfully provided descriptors for drives /dd, /d0, /d1, and /d2 in 80 track double-sided format. All you need to do here is make a new bootfile with the proper descriptors installed. HARDWARE -------- The 3.5 inch drives use a different cable connector than the 5 1/4 inch units. These are a 34 pin dual-header type connector with the same pin-out as the 34 pin edge card type. HOWEVER, these drives are also capable of receiving their DC power through the ribbon cable, which is how Tandy powers them in their new computer line. There is also a 4 pin power connector that my be used instead. But, DO NOT provide power using the 4 pin power plug without removing some of the pins from the 34 pin header type ribbon connector. If you do, you will be grounding the power supply through the disk controller card which will result in some major damage to the power supply, the controller card, or both. If you use the 4 pin power connector, you must pull all the ODD number pins from the connector, i.e., pins 1,3,5,7....etc. None of these lines are used for any disk control signals so don7t worry about that. Addendum: Not all 3.5 inch drive manufacturers provide power to the 34 pin connector. On those drives that don't, there is no need to remove any pins. However, if you are not sure, remove them anyway to protect your power supply in case you are wrong. The 4 pin power connector is wired in the same was as the older drive connectors, with 12VDC on one end pin, 2 middle pins for ground, and 5VDC on the other outer pin. You should ake sure which outer pin is for 12V and which is for 5V before providing power to them or damage will result. My drive was marked for the proper pins, but some may not be. INSTALLATION ------------ Being a practical minded (i.e. CHEAP) person, I installed my drive in a small experimentors box, and tapped the power and the 34 pin connector off my current dual disk drive package. Unless your current drives over-tax the unit's power supply, this should be safe as they use so little power themselves. So far, I have not noticed any power problems nor any increase in the heat output of the power supplies voltage regulators. I haven't yet measured the current draw, but I expect it to be very small. The 34 pin ribbon cable connector was easy to find at the local Radio Shack store, but the 4 pin power connector was not. So, I took another header connector and cut it down to only 4 pins and used that for now. Later, I suppose I'll get the "proper" one, but it's been working fine. You should buy a new 34 pins ribbon cable and three 34 pin edge card connectors that are designed to clamp on the cable. Measure at what points you need to add the one or two connectors for your current drives, and then add whatever lenght is required to extend the cable to the location of the 3.5 inch drive. Then, simply clamp the connector on. I installed the drive on my system as drive /DD and am surprised that is it noticably faster than my older drives. I then set the step rate to 6 ms using DMODE, saved the changed descriptor back to disk, and COBBLER'd a new boot. At this step rate, all they do is "buzz" a little when accessing. Eventually, I'll get another and have 1.4 meg of storage in these two tiny units. The disks themselves are much easier to use, you need not be as careful with them as floppies, and the are just neater! I feel like I just discovered disk drives for the first time again. Hope this helps some. /\/\ark Usenet ....!uflorida!ki4pv!macs!stetson!rewop!sysop UUCP direct (904) 736-1849 rewop!sysop Internet griffith@stetson.bitnet