IA88C00-PLC68I-R datasheet(22/80 Pages) INNOVASIC

22 / 80 page

IA88C00

Data Sheet

Microcontroller

As of Production Version -01

ENG 21 0 050519-00

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Innovasic Semiconductor

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The Stack Pointer always points to data stored on the tip of the stack. The address is decremented prior to

a PUSH and incremented after a POP.

The stack is also used as a return stack for CALLS and interrupts. During a CALL, the contents of the PC

are saved on the stack to be restored later. Interrupts cause the contents of the PC and FLAGS to be saved

on the stack for recovery by IRET when the interrupt is finished.

When configured for internal stack (using the register file), R217 contains the Stack Pointer. R216 can be

used as a general purpose register. However, its contents will be changed if an overflow or underflow

occurs as the result of incrementing or decrementing the stack address during normal stack operations.

A user-defined stack can be implemented in both the register file and program or data memory. These can

be made to increment or decrement on a push by the choice of opcodes. For example, to implement a

stack that goes from Low addresses to High addresses in the register file, use PUSHUI and POPUD. For a

stack that goes from High address to Low addresses in data memory, use LDEI for POP and LDEPD for

PUSH.

Figure 14. R217 (D9) SPL Stack Pointer

Bit

SP7

SP6

SP5

SP4

SP3

SP2

SP1

SP0

Initial Value

Read/Write

R/W

Stack operations are supported in the register file or in data memory. Bit 1 in the external Memory Timing

R217 is the LSB.

The Stack Pointer always points to data stored on the tip of the stack. The address is decremented prior to

a PUSH and incrementd after a POP.

The Stack is also used as a return stack for CALLS and interrupts. During a CALL, the contents of the PC

are saved on the stack to be restored later. Interrupts cause the contents of the PC and FLAGS to be saved

on the stack for recovery by IRET when the interrupt is finished.

When configured for internal stack (using the register file), R217 contains the Stack Pointer. R216 can be

used as a general purpose register. However, its contents will be changed if an overflow or underflow

occurs as the result of incrementing or decrementing the stack address during normal stack operations.

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