Operations With The Base Address Register (Br Register) - Siemens CPU 948 Programming Manual

Operations with the Base Address Register (BR Register)

9.4 Operations with the Base Address Register (BR Register)
Application
Operations
Changing the BR register
9 - 22
The base address register (20 bits) allows you to calculate addresses
and use indirect register load and transfer operations without using the
ACCUs.
The memory location whose absolute address is calculated as the sum
of the BR register content plus a constant is accessed.
Absolute address = BR register content + constant
Table 9-6 Load and arithmetic operations with the BR register
Operation Operand
MBR Constant
(0H to
F FFFFH)
ABR Constant
(-32 768 to
+32 767)
• • The BR register is retained, when the program is continued in a
different block of the same program execution level due to a
jump statement ('JU FB'/'JC FB').
• • The BR register is retained after nesting in a different program
execution level.
• • If a different program execution level is called by the system
program, the BR register is set to '0'.
Function
Load the BR register with a
20-bit constant
Add a 16-bit constant to the contents
of the BR register
CPU 948 Programming Guide
C79000-G8576-C848-04