Micronas SDA 6000, User Manual

Page: 82 / 412

SDA 6000
PRELIMINARY DATA SHEET
Version 2.1
C16X Microcontroller
4 - 51 Micronas
(usually bigger) can be realized via software. This mechanism is supported by the
STKOV and STKUN registers (see respective descriptions below).
The SP register can be updated via any instruction, which is capable of modifying an
SFR.
Note: Due to the internal instruction pipeline, a POP or RETURN instruction must not
immediately follow an instruction updating the SP register.
SP Reset Value: FC00
H
The Stack Overflow Pointer STKOV
This non-bit addressable register is compared against the SP register after each
operation, which pushes data onto the system stack (e.g. PUSH and CALL instructions
or interrupts) and after each subtraction from the SP register. If the contents of the SP
register are less than the content of the STKOV register, a stack overflow hardware trap
will occur.
Since the least significant bit of register STKOV is tied to ‘0’ and bits 15 through 12 are
tied to ‘1’ by hardware, the STKOV register can only contain values from F000
H
to
FFFE
H
.
STKOV Reset Value: FA00
H
The Stack Overflow Trap (entered when (SP) < (STKOV)) may be used in two different
ways:
• Fatal error indication treats the stack overflow as a system error through the
associated trap service routine. Under these circumstances data in the bottom of the
Bit Function
sp Modifiable portion of register SP
Specifies the top of the internal system stack.
Bit Function
stkov Modifiable portion of register STKOV
Specifies the lower limit of the internal system stack.
1 0 1
5 4 3 2 1 0 11 10 9 8 7 6 15 14 13 12
r rw r r r
1 1
r
sp
1 0 1
5 4 3 2 1 0 11 10 9 8 7 6 15 14 13 12
r rw r r r
1 1
r
stkov