Oscar Oberg <Oscar.Oberg@abc.se> wrote:
> Got a description of how to make one for me?
   
   Sure. If you look at the KA410 system board, you'll see three shrouded
header connectors close together: a 50-lead one, a 60-lead one, and a 20-
lead one. The 50-lead one is the SCSI bus coming out of the SCSI
controller. What comes out of the MFM controller are the 60-lead connector
and the 20-lead one. This controller can control one floppy disk drive
(FDD) and two Winchester disk drives (WDDs). This would normally require 4
connections: floppy control&data, Winchester control, Winchester data for
drive 0, and Winchester data for drive 1. Normally each would be a separate
cable/connector. DEC, however, has bunched the first three into the 60-lead
connector, and only the last one is a separate connector with the industry
standard pinout (that's the 20-lead one).
   
   The ribbon cable coming out of the 60-lead connector is first split
(cut) into three sections, corresponding to the three logically separate
connections described above. The first 28 conductors form the floppy
control&data section, the next 21 form the Winchester control section, and
the last 11 form the Winchester data section for drive 0. Each of them goes
to an edge connector that connects to the respective drive. The industry
standard cable for each of the three has more conductors than what you get
by splitting the 60-conductor cable as described above. The order of the
leads on the DEC cable is the same as on the industry standard connector,
but some leads on the latter that DEC doesn't use are skipped on the
former. Therefore, before crimping on each edge connector, you have to cut
the cable coming to it again and connect the resulting sections to the
connector's leads leaving gaps where necessary. The following leads are
skipped: 3-6 and 13-14 on the floppy control&data section, 1, 3, 7, 11, 15-
17, 21, and 25-29 on the Winchester control section, and 3-4, 6-8, 10-11,
15, and 20 on the Winchester data for drive 0 section.
   
   This way you'll get the cable that DEC puts in VS2000s without expansion
adapters. It will work fine if you don't need WDD 1. If you do need it,
however, you'll need to make the cable that DEC puts in VS2000s with
expansion adapters and MV2000s (which always have these adapters). DEC has
intended WDD 1 to be external, so the connection to it is in the expansion
adapter (a pizza-box that screws into the bottom of the system unit).
Inside this pizza-box there is a board which on one side has the external
ST-506/412 connector extending outside the unit and on the other side has
the internal connectors for WDD 1 control and data. The data connector has
the standard pinout, but it is header, not card edge. A straight 20-
conductor ribbon cable with header connectors on both ends connects this
thing to the system board. The control signals are connected by extending
the Winchester control section of the 60-conductor cable beyond the edge
connector and into the expansion adapter. The interface board has a 26-lead
header connector for this, and the 5 last leads are unused. The first 21
comprise the abovenoted section, which has exactly this many conductors.
   
   Sincerely,
   Michael Sokolov
   Phone: 440-449-0299
   ARPA Internet SMTP mail: sokolov@alpha.ces.cwru.edu