Hi Kevin,
output after boot:
R0 R4 SP PC(at time of boot initiated)
$
boot device codes, suffix n for unit number n, n=0,1,..., empty=0
TT terminal paper tape
DK RK11 moving head cartridge
DT DECtape
MT TM11 magtape (7 or 9 track, 800 BPI, odd parity, dump mode)
DP RP11 moving head disk pack
CT TA11 cassettes
PR PC11 high-speed paper tape reader
DX RX11 diskette
some M9301 versions additionally support MASSBUS devices.
DX<cr> should work fine for you.
The DX boot appears to be at address 173546. I will fax the
program code at that address. Do you have the RX11 controller register
descriptions ?
John