Atari 1050 US Doubler with a triple OS enhancement.

[TZJB]

Based on my experience with my own triple OS Lazer enhanced drives I came up with an idea to improve my 1050 US Doubler enhanced disk drive and add a 'triple' operating sytem.

 

A standard Atari 1050 disk drive can only achieve an enhanced formatted capacity of 130KB on a standard single sided double density floppy disk. Whereas the main advantage of a USD drive enhancement is not necessarily the speed improvement, but to improve formatted disk capacity to full double density 180KB SSDD.

 

This 1050 disk drive had the enhancement installed over 40 years ago, but the US Doubler lacks any real diagnostic software support, so I added back the original 1050 Rev L software as an option.

 

This is really easy with a 2764 EPROM as you just need to common pins 26, 27, 28 and pin 1 together which connects to +5V via the onboard IC socket pin 24. With a 10K pullup resistor on pin 2 A12 and a switch to ground it is a simple substitute for the original 24 pin EPROM. Offset the new EPROM with the four pins 1 & 2, 27 & 28 overhanging the 24 pin socket and it all fits nicely.

 

Dual OS Atari 1050 Rev.L& ICD USD Rev.L 000DE3C8.064.zip

 

 

To avoid damaging the EPROM, I did all the soldering connections onto two 14 pin SIL sockets that I broke off from a 40 pin SIL socket using a dead 28 pin chip as a former. This leaves space for the resistor and wiring.

 

 

At the time I did not take any pictures of the 2764 EPROM as I came up with another idea.

 

I needed to add a switch to the 1050 case so I thought I may as well go for a three position switch and 3 operating systems, like with the Lazer, but what for the third?

 

Then it occured to me that the 1050 disk drives default to D1: - D4: so why not have an option for D5: - D8: for the third OS?

 

I edited the USD ROM by adding 4 to each disk drive number in the header, then made the 27128 EPROM image, but testing became a problem due to +5V VCC on the socket pin 24 clashing with the extra address A13.

 

I decided to cut that pin off to isolate it from +5V VCC and add the second 10K resistor pullup to it, then source the +5V VCC directly by soldering to the decoupling capacitor.

 

TriOS__USDRevL USDRevL5-8 1050RevL.128.zip

 

Here is the sequence:-

 

 

The write protect LED becomes the power LED as it is bi-colour green/red and the old power LED position houses the triple OS switch which is now left for USD, middle for 1050 and right for USD D5: - D8:

 

The right hand switches select the disk drive numbering dependant on the loaded operating system. The power does need to be cycled to select the individual operating systems.

 

With the SIO filter capacitors also removed, this can be used in combination with any modern HSIO disk drive replacement with the advantage of the optional extended drive numbering, plus diagnostic software support with the standard OS.