Technical data

9.4 Operations with the Base Address Register (BR Register)
Application The BR register (base address register, 32 bits) is used by the load and
transfer operations described from Section 9.3.3 onwards to address
the memory. The absolute address of the memory cell to be accessed
is calculated as the sum of the contents of the BR register and a
constant as follows:
Absolute address = BR register contents + constant
Operations
Operation Operand Function
MBR
ABR
Constant
(0H to
F FFFFH)
Constant
(-32 768 to
+32 767)
Load the BR register with a
20-bit constant
1)
Add a 16-bit constant to the contents
of the BR register
1)
Bits 2
20
to 2
31
of the BR register are set to "0".
Changing the BR register •• The BR register is retained when the same program processing
level is
continued in another block called by the jump operation
(JU FB / JC FB).
•• The BR register is retained after nesting in a different program
execution level.
When the system program calls
another program processing level,
the BR register is set to "
0".
MBR 0 to FFFFF
0.........0
BR
20-bit constant
ABR -32768 to +32767
BR
BR
16-bit constant
(fixed point number)
31 19 0
31 0
31 0
Fig. 9-10 Loading the BR register
Table 9-5 Load and arithmetic operations with the BR register
Operations with the Base Address Register (BR Register)
CPU 928B Programming Guide
9 - 26 C79000-B8576-C898-01