Virtual SIO OR "How to have virtually any number of boot and data disks on the ST."

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OVERVIEW:
Of course, I'd much rather have an easy to use and plug in hard drive, but thats still in the works. With a simple interface and some cable/connectors, software on the ST will look like disk drives running from the SIO port, only faster. The software I have found(via Doctor Clu), is 800XLDJ, and it does that. It lets you create disk images in many different formats. You can then have up to 8 active, replacing physical drives that are not turned on, or don't exist. While its called 800XLDJ, I see no reason why it can't be used with any 8 bit Atari.
Find it at:DJ800.html 380K zip.(16jun2k RLD), also at: umich archive


Note that throughout this section, I'll refer to any setup that allows the SIO drives to be emulated for use by a real Atari8 as V~S(Virtual SIO). This is because this info can be used with an ST(800XLDJ) and a DOS-PC(APE, SIO2PC) using compatible hardware and software. The hardware uses pins 2, 3, 7, & 22 on a DB25 connector, on the ST and PC. AND NOTE, THIS INVOLVES SOLDERING CHIPS, CABLE, AND CONNECTORS. DO SO AT YOUR OWN RISK. YOU ARE RESPONSIBLE FOR ANY HARDWARE DAMAGE AND SOFTWARE LOSS RESULTING FROM THIS. THOUGH I BELIEVE THIS TO BE VERY STABLE.

EASIO-S cables:
One need is to be able to switch a computer between sets of A8 peripherals, or switch peripherals between several computers. SIO connectors are non standard, expensive, and somewhat difficult to turn into a useable switch box. For about $10.00, standard DB25 switch boxes are common, and lets you choose 2 to 5 items. So I decided to make up SIO cables that have a DB25M connector on one end, just to plug into these switch boxes. Pin numbering is the same on both, leaving the 12 bottom pins on the DB25 unsed. Just one of the cables is needed for each computer and peripheral set that needs to be switched. I also made a similar cable that plugs into the back of an A8 printer interface and connects to a DB25 switch box. Switching between printers is now a snap

The picture shows a peripheral cable(A), A8 cable(common), and V~S adapter(B).

800XLDJ PROBLEMS:
Disk images at least work. Ignoring calls to existing drives doesn't work. And creating virtual hard drives(to 16 megs) always gives an FOPEN error. Also, since the program and developer are german/polish, its no surprise that the program window is designed for monochrome monitors, so when used on color monitors, the bottom is cut off, and it can't be sized. These days there is no excuse for not creating a program that is well behaved in both mono and color! O.K. Graphics files and most Games will look bad in mono, no matter what.

And, all of the info(i.e. bug reports) are in German. No real docs. I found my info by trial and error, and by trying to read the gibberish that german-to-english translate programs provide. These days, with a small tight community, there is no excuse for not creating docs in English. Even bad english-someone(me) will help correct it.

APE PROBLEMS:let me know of any.
SIO2PC PROBLEMS:let me know of any.

SPEED
Atari A8	Ramdisk	800XLDJ 8mHz Mega ST(1)	SIO2PC 486/100 (2)	APE
(R)Booting Paperclip (155 dd sectors) in 41S, ~956 bytes/sec using ATR8000 drives.
(R/W)copying 73375 bytes in 1M34 is ~777 bytes/sec using ATR8000 drives.
	(R/W)copying 73375 bytes in 51S is ~1438 bytes/sec.
(R)Booting Paperclip (155 dd sectors) in 27S, ~1452 bytes/sec.
	(R/W)copying 73375 bytes in 48S is ~1528 bytes/sec.
(R)Booting Paperclip (155 dd sectors) in 25.7S, ~1525 bytes/sec.
	ramdisk not yet tested.
boot not yet tested.

Set the com port to 19200 baud.
(1)Tested with one hundred feet of cable. The ST serial port(and printer port)easily gets confused, so rebooting has been a constant need. It may be possible to write another emulator program that resets the port after every drive access. However, once working, it does very well. Using the high speed port actually made it worse.
(2)Tested with ten feet of cable. I could not get this to work using a DOS window in win95, but dropping to the dos prompt, the program worked very well. Setting the com port to 115K, booting Paperclip took the same time. Now if I could find a way to make it run in more than 640K of ram(I think there is a switch). Next test is with XF551 high speed.

Other Notes:
The maximum the SIO port will do normally, is about 2000 bytes/sec with 1920 bytes/s rated as typical, but I heard that its possible to manually run the sio port using much higher baud rates. All transfers have some non-data overhead.

While it may be possible to use a DOS that understands warp I/O, I don't think 800XLDJ does, and it probably wouldn't be any faster, unless direct handling of SIO baud rates changes that(but that is only useful for standard DOS programs or changed OS roms.). V~S can already buffer the data from the ST harddisk and pass it to the A8 faster than a physical drive, so its limitations are mostly speed of ST of code used.

And the ATR-8000 uses a faster format interleave than do 810s, 1050s, and most other A8 drives, so I didn't test any other in standard mode. This speed is noticeable when the disks are used on any drive.

Even though its a ramdisk, there is a copy phase that slows down transfer. A program designed to directly write to banks would be faster.

ON TO PAGE TWO: Creating the disk images----->      ON TO PAGE THREE: Cabling and More----->