booting from RQDX3

From: Jonathan Engdahl <>
Date: Fri Jun 1 13:45:37 2001

Putting a ROM on the disk controller at 173000 is the usual way
of doing it, but here's a slick alternative that is used on the
DSD 4140 floppy controller:

There is no ROM onboard other than the microcode for the AMD
2901 (one 4-bit slice!), but there is a single register mapped
onto the Qbus at 173000. If the PDP-11 jumps there, the
controller gives back a jump-to-self opcode. While the PDP-11 is
busy chewing on that, the 2901 sees what has happened and copies
sector zero from the floppy to address zero via DMA, then it
changes the contents of 173000 to "CLR PC", which causes the
PDP-11 to execute the boot code.

So just because you don't see ROMS doesn't meant the board can't

Jonathan Engdahl             Rockwell Automation
Principal Research Engineer  24800 Tungsten Road
Advanced Technology          Euclid, OH 44117  USA
Euclid Labs        
Received on Fri Jun 01 2001 - 13:45:37 BST

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