That's what I thought, a disk doubler like they used to sell on TRS 80's.
b
On Wed, Feb 12, 2020 at 5:21 PM William Sudbrink via cctalk <
cctalk at classiccmp.org> wrote:
  Interesting daughter board on the 4FDC in this ebay
lot:
 
https://www.ebay.com/itm/Vintage-Lot-of-2-Cromemco-S-100-Boards-Z80-ZPU-CPU-
 4FDC-Floppy-Disk-Controller/202903187221?hash=item2f3df8ef15:g:kGQAAOSwhKZeQ
 z9C
<https://www.ebay.com/itm/Vintage-Lot-of-2-Cromemco-S-100-Boards-Z80-ZPU-CPU-4FDC-Floppy-Disk-Controller/202903187221?hash=item2f3df8ef15:g:kGQAAOSwhKZeQz9C>
 (sorry if you have to paste the URL back together)
 I thought maybe it was the JVB FDCX4 but after looking at some pictures,
 it clearly is not.  Looks like it just adds a data separator to the 1771?
 Anybody
 have one of these?
 Bill S.