XXDP on a really small system?

I have an 11/03 (unmapped, of course) with 28kW memory and two DLV11s. I'm trying to build an XXDP image on TU58 that I can boot on this system, using an XXDP 2.5 RL02 image and simh. My simh configuration is - CPU 11/03, NOEIS, NOFIS, BEVENT disabled, autoconfiguration enabled, idle disabled . TTI address=17777560-17777563, vector=60, BR4 TTO address=17777564-17777567, vector=64, BR4 TDC controllers=1, address=17776500-17776507, vector=300*, BR4, 2 units . RL RLV12, address=17774400-17774411, vector=160, BR5, 4 units I can boot from the RL02 OK - MEMORY MANAGEMENT UNIT NOT FOUND BOOTING UP XXDP-SM SMALL MONITOR XXDP-SM SMALL MONITOR - XXDP V2.4 REVISION: D0 BOOTED FROM DL0 28KW OF MEMORY NON-UNIBUS SYSTEM RESTART ADDRESS: 152010 TYPE "H" FOR HELP But running UPDAT to create a new system image on the TU58 dies .R UPDAT UPDAT .BIC HALT instruction, PC: 000010 (000012) If I change the CPU to an 11/23 (but keep the same memory and other configuration) then UPDAT works. Is there some issue or limitation in running XXDP on a 11/03? Is it just UPDAT that doesn't work, or are there bigger problems? Thanks Bob