SDA5250 Datasheet, PDF (48/143 Pages) Siemens Semiconductor Group – TVTEXT 8-Bit Microcontroller

SDA 525x
Register Addressing
Register addressing accesses the eight working registers (R0 – R7) of the selected
register bank. The PSW-register flags RS1 and RS0 determine which register bank is
enabled. The least significant three bits of the instruction opcode indicate which register
is to be used. ACC, B, DPTR and CY, the Boolean processor accumulator, can also be
addressed as registers.
Direct Addressing
Direct byte addressing specifies an on-chip RAM-location (only low part) or a special
function register. Direct addressing is the only method of accessing the special function
registers. An additional byte is appended to the instruction opcode to provide the
memory location address. The highest-order bit of this byte selects one of two groups of
addresses: values between 0 and 127 (00_H – 7F_H) access internal RAM-locations, while
values between 128 and 255 (80_H – 0FF_H) access one of the special function registers.
Register-Indirect Addressing
Register-indirect addressing uses the contents of either R0 or R1 (in the selected
register bank) as a pointer to locations in the 256 bytes of internal RAM. Note that the
special function registers are not accessable by this method.
Execution of PUSH- and POP-instructions also use register-indirect addressing. The
stack pointer may reside anywhere in internal RAM.
Immediate Addressing
Immediate addressing allows constants to be part of the opcode instruction in program
memory.
An additional byte is appended to the instruction to hold the source variable. In the
assembly language and instruction set, a number sign (#) precedes the value to be used,
which may refer to a constant, an expression, or a symbolic name.
Base-Register plus Index Register-Indirect Addressing
Base-register plus index register-indirect addressing allows a byte to be accessed from
program memory via an indirect move from the location whose address is the sum of a
base register (DPTR or PC) and index register, ACC. This mode facilitates accessing to
look-up-table resident in program memory.
Semiconductor Group
48
1998-04-08