Lpc2000

I'm trying to set EXTINT0 to active-high, edge-sensitive (i.e. set 
EXTPOLAR and EXTMODE to 1), but am unable to set/read back bit 0 in 
either of the registers.  FWIW, bit 1 (for EXTINT1) sets/reads back 
successfully.  

The code sample below looks correct.  Does anyone have any ideas?

	byte b=EXTPOLAR;
   	E3A0320E   mov r3, #0xE0000000
   	E283397F   add r3, r3, #0x001FC000
   	E3A02F53   mov r2, #0x0000014C
   	E7D33002   ldrb r3, [r3, r2]
   	E54B300D   strb r3, [r11, #-13]
	EXTPOLAR = 1; // set EXTINT0 active high
   	E3A0220E   mov r2, #0xE0000000
   	E282297F   add r2, r2, #0x001FC000
   	E3A01F53   mov r1, #0x0000014C
   	E3A03001   mov r3, #0x00000001
   	E7C23001   strb r3, [r2, r1]
	b=EXTPOLAR;	
   	E3A0320E   mov r3, #0xE0000000
   	E283397F   add r3, r3, #0x001FC000
   	E3A02F53   mov r2, #0x0000014C
   	E7D33002   ldrb r3, [r3, r2]
   	E54B300D   strb r3, [r11, #-13]
	b=EXTMODE;	
   	E3A0320E   mov r3, #0xE0000000
   	E283397F   add r3, r3, #0x001FC000
   	E3A02F52   mov r2, #0x00000148
   	E7D33002   ldrb r3, [r3, r2]
   	E54B300D   strb r3, [r11, #-13]
	EXTMODE = 1; // set EXTINT0 edge-sensitive
   	E3A0220E   mov r2, #0xE0000000
   	E282297F   add r2, r2, #0x001FC000
   	E3A01F52   mov r1, #0x00000148
   	E3A03001   mov r3, #0x00000001
   	E7C23001   strb r3, [r2, r1]
	b=EXTMODE;	
   	E3A0320E   mov r3, #0xE0000000
   	E283397F   add r3, r3, #0x001FC000
   	E3A02F52   mov r2, #0x00000148
   	E7D33002   ldrb r3, [r3, r2]
   	E54B300D   strb r3, [r11, #-13]