
As Shane Nay once pointed out, if you hose the PMON partition of
your VR3's flash, you will have made a rather lovely brick.  There's
no going back if you screw up PMON.  This is why should you write
protect the PMON partition with the following instructions.  This
will prevent you from screwing up and accidentally making your VR3
permanently unusable.  Please follow these instructions extremely
carefully.

First you have to get to the PMON prompt.  Usually you do this by
starting minicom, hyperterm, etc with the following settings:

o  Baud:  115200bps
o  Bits, parity, stop:  8N1
o  Flow control:  hardware or none

Now reset your agenda, and hit ENTER within the first three seconds
of the boot.  You should then be at a PMON> prompt.  Now you can
enter the following commands to write protect or unprotect your
PMON.  

-----------------------------------------------------------------

To WRITE PROTECT your PMON, these are the instructions:

m -b bfc00000 60
m -b bfc00000 01
d -b bfc00000
  (Should display 80 00 80 00, etc.)
  Type 'q' to stop the display

m -b bfc00000 ff
m -b bfc20000 60
m -b bfc20000 01
d -b bfc20000
  (Should display 80 00 80 00, etc.)
  Type 'q' to stop the display

m -b bfc20000 ff

-----------------------------------------------------------------

To WRITE *UN*PROTECT your PMON, these are the instructions:

NOTE:  
   You should only unprotect PMON if you are about to
   flash upgrade the PMON binary on your Vr3.  Otherwise, 
   at all times, you should have PMON write protected so 
   you don't accidentally brickify your VR3. 

m -b bfc00000 60
m -b bfc00000 D0
d -b bfc00000
  (Should display 80 00 80 00, etc.)
  Type 'q' to stop the display

m -b bfc00000 ff
m -b bfc20000 60
m -b bfc20000 D0
d -b bfc20000
  (Should display 80 00 80 00, etc.)
  Type 'q' to stop the display

m -b bfc20000 ff

-----------------------------------------------------------------

Lastly, here's the output from a session where I protected 
PMON using minicom.  AFAIK, your output should be very close
if not identical:

PMON version 3.1.272 [NEC Vr41XX UEB,EL,FLASH]
VR4181 support by Bradley D. LaRonde <brad@ltc.com> Mar 18 2001 13:58:05
This is free software, and comes with ABSOLUTELY NO WARRANTY,
you are welcome to redistribute it without restriction.
CPU type NEC VR4181                     
  Rev 5.2.  65.54 MHz/1.17 MHz.         
Memory size   8 MB.                     
Icache size  16 KB, 16/line             
Dcache size   8 KB, 16/line             
                                        
                                        
Autoboot command: "g -e bf0005e0 -- root=/dev/rom
video=vr4181fb:xres:160,yres:"
Press any key to cancel.
 2
PMON>                                                                           
PMON> m -b bfc00000 60                                                          
PMON> m -b bfc00000 01                                                          
PMON> d -b bfc00000                                                             
bfc00000  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
bfc00010  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
bfc00020  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................
bfc00030  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
bfc00040  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
bfc00050  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
bfc00060  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
bfc00070  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
bfc00080  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
bfc00090  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
PMON> m -b bfc00000 ff                                                          
PMON> m -b bfc20000 60                                                          
PMON> m -b bfc20000 01                                                          
PMON> d -b bfc20000                                                             
bfc20000  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
bfc20010  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
bfc20020  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
bfc20030  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
bfc20040  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
bfc20050  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
bfc20060  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
bfc20070  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
bfc20080  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
bfc20090  80 00 80 00 80 00 80 00  80 00 80 00 80 00 80 00   ................   
PMON>                                                                           
PMON> m -b bfc20000 ff                                                          

Good luck,
Jeff
