D950-CORE datasheet(24/89 Pages) STMICROELECTRONICS

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D950-Core

Immediate Data Addressing

This mode allows direct register loading. If the data is 16-bit long (see LR and LL bits of STA

Immediate short data addressing is possible on 6-bit data, without instruction extension:

If AXi, AYi or STA are concerned, the 6 LSB’s are loaded from the instruction and the MSB’s

are unchanged. For all other registers, the MSB’s are fed with 0

Figure 4.10

Immediate Addressing

Stack operation addressing

16-bit Stack Pointer register SPX is available for X-memory space and SPY for Y-memory

space. It can be initialized to any value, provided it points to a stack dedicated memory area.

The stack size is limited to the available memory. No provision is taken to detect stack

overflows or underflows. After reset, the SP registers are not initialized.

The following addressing modes are possible with the 16-bit SP registers:

•

For the X and Y stack pointer registers: PUSH (SP pre-decrement) or POP (SP

post-increment) for register-to-stack move, memory-to-stack move and for

immediate value-to-stack move.

Double PUSH and double POP. In this operation, the PUSH or POP operation

is performed simultaneously on the X and Y stack point register. This is used in

a switching context.

•

For the X stack pointer register only: Indirect indexed addressing for register-

to-stack move.

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