ST63126 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'ST63126' PDF : 86 Pages View PDF
ST63140,142,126,156
ST631xxx CORE (Continued)
Stack
The ST631xx Core includes true LIFO hardware
stack that eliminates the need for a stack pointer.
The stack consists of six separate 12-bit RAM loca-
tions that do not belong to the data space RAM
area. When a subroutine call (or interrupt request)
occurs, the contents of each level is shifted into the
next level while the content of the PC is shifted into
the first level (the value of the sixth level will be
lost). When subroutine or interrupt return occurs
(RET or RETI instructions), the first level register is
shifted back into the PC and the value of each level
is shifted back into the previous level. These two
operating modes are described in Figure 6. Since
the accumulator, as all other data space registers,
is not stored in this stack the handling of this regis-
ters shall be performed inside the subroutine. The
stack pointer will remain in its deepest position, if
more than 6 calls or interrupts are executed, so
that the last return address will be lost. It will also
remain in its highest position if the stack is empty
and a RET or RETI is executed. In this case the
next instruction will be executed.
Figure 6. Stack Operation
RET OR RETI
WHEN
OCCURS
PROGRAM COUNTER
STACK LEVEL 1
STACK LEVEL 1
STACK LEVEL 1
STACK LEVEL 1
STACK LEVEL 1
STACK LEVEL 1
WHEN CALL
OR
INTERRUPT REQUEST
OCCURS
VA000424
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