DTC 520A - SASI or SCSI?

From: Richard Erlacher <edick_at_idcomm.com>
Date: Wed Dec 15 02:43:15 1999

I'm currently the victim of severe abuse from the significant other . . .
she's insisted I put my toys away . . .

In the process, I just an hour or so ago had the manual for this controller
series in my hands. Having looked at both the manuals, 510 and 520, I find
mention of neither SASI nor SCSI. The signal definition seems to track SCSI
except for pin 42 which they call TDN, which is a new one on me. The manual
doesn't seem to define this signal. Maybe its TBD??? The board supports
parity, which, IIRC, SASI didn't. It supports both floppy and hard disks of
the 5-1/4" flavor, with MFM on the HD and either FM or MFM on the floppy.

It's late and I'm too pooped to sit down and scan the approximately 25 pages
of manual for you, particularly since the PC with the scanner is in pieces
for transit to the basement. I'll see about getting it scanned in the next
few days, but keep in mind it's a really poor Xerox copy, some lines of text
in several places being completely illegible. The fact that I have these
manuals suggests that DTC was a major competitor in the bridge-controller
market, else I'd have probably ignored them.

For the last couple of weeks I've been kicking the SCSI vs. SASI thing
around with Don Maslin and Allison Parent in the Ampro Little Board context,
and, as Allison clearly pointed out to me, the SCSI drivers Ampro provided
seems to operate a few of the garden-variety SASI controllers just fine.

I'd conclude from my observations in going through AMPRO's code and from
Allison's comments, that the hardware differences are probably irrelevant in
the early-'80's context.

Some controllers have a software reset, but not all, and since you have to
option of doing a hardware reset, I guess that won't be missed.

They didn't have a standard "common command set" back then, so you'll have
to commune with your muse to devise a driver. I have had absolutely no luck
with the various ADAPTEC, OMTI, and XEBEC bridges I have in conjunction with
a PC-based controller.

Other things I've found in the current spelunking expedition:

        Tarbell S-100 FDC (1771) manual
        XCOMP manual for ST-R bridge controller to HDD
        CompuPro Econoram SRAM Board manual (model??? ... 16K of 2147's)
        CDC 6000-series Assembler (COMPASS) manuals for SCOPE OS.
        Visual 200 Manual
        Visual 50 manual
        more Intel ISIS-II and IRMX manuals
        Pascal-Z v4.0 manual


-----Original Message-----
From: Ethan Dicks <ethan_dicks_at_yahoo.com>
To: Discussion re-collecting of classic computers
Date: Wednesday, December 15, 1999 12:32 AM
Subject: DTC 520A - SASI or SCSI?

>Going through a box of disk interface cards, I ran across a couple of these
>DTC 520As. Cursory examination shows a 50-pin connector (J4) with two
>termination resistors (220/330), two 20-pin connectors (J2, J3) which are
>presumably analog data for two ST506 drives and two 34-pin connectors (J1
>and J9). I would expect that J1 is the control cable that goes with J2 and
>J3. I suspect that J9 is for floppies. The major chips are two 8255s, one
>8085, one DTC-037, one NEC D765, one FDC-043, one DTC MSA 2827G, an AMD
>and an AMD AM9517. There are several chips with the numbers covered by
>written numbers, PALs and ROMs, no doubt.
>There are 8 LEDs in a row by the power connector and an 8-position DIP
>>From the date codes, it appears to have been made near the end of 1983.
>Can anyone shed any additional light on this device? Knowing what this was
>expecting to hook up to and how to set the DIP switches would be a great
>Many thanks,
>Infinet has been sold. The domain is going away in February.
>Please send all replies to
> erd_at_iname.com
>Do You Yahoo!?
>Thousands of Stores. Millions of Products. All in one place.
>Yahoo! Shopping: http://shopping.yahoo.com
Received on Wed Dec 15 1999 - 02:43:15 GMT

This archive was generated by hypermail 2.3.0 : Fri Oct 10 2014 - 23:31:55 BST