Page 374 - Introduction to Microcontrollers Architecture, Programming, and Interfacing of The Motorola 68HC12

12.1 The 68.11 351

because the 6811 has only an 8-bit offset. You often have to calculate the address
explicitly as the effective address is calculated within the 6812 instruction, put this
effective address in the X register, and use the instruction LDAA 0, X. Also, index
arithmetic can be done in accumulator D; the 6811 has the instruction XGDX to move
the result to and from X.
The 6812 LBRA and other 16-bit branch instructions, which simplify the writing of
position-independent code, are missing in the 6811, Writing position-independent code is
tedious. However, except for this capability, the 6811 can get the effect of long branch

Table 12.1. Instruction Set and Addressing Modes of the 6811