IP2022 User’s Manual—Instruction Set Architecture www.ubicom.com 65 Figure 3-3 shows the direct addressing mode used to reference
the  global  registers.  This  mode  is  distinguished  from  the  mode
used to access the special-purpose registers with bit 7 of the “fr”
field.  Because  these  registers  have  this  additional  addressing
mode  not  available  for  the  other  registers,  they  are  especially
useful for holding global variables and frequently accessed data. Figure 3-3  Direct Addressing, Global Registers 3.1.3 Indirect Addressing Indirect addressing is used when all of the bits in the “fr” field are
clear. The location of the operand is specified by a 12-bit pointer
in the IPH and IPL registers. The upper four bits of the IPH register
are not used. Addresses from 0x000 to 0x01F cannot be accessed
reliably with this addressing mode, therefore it must not be used
for  this  purpose.  (Direct  addressing  should  be  used  instead.)
Figure 3-4 shows indirect addressing. 515-008.eps             128
Global Registers 7 0   9-Bit "fr" Field
from Instruction 0 8 1 n n n n n n n 0 7 6