mc9s12c32mpb16 Freescale Semiconductor, Inc, mc9s12c32mpb16 Datasheet - Page 125

• Manufacturer Part Number: mc9s12c32mpb16
• Description: Hcs12 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

The PPAGE register holds the page select value for the program page window. The value of the PPAGE
register can be manipulated by normal read and write (some devices don’t allow writes in some modes)
instructions as well as the CALL and RTC instructions.
Control registers, vector spaces, and a portion of on-chip memory are located in unpaged portions of the
64K byte physical address space. The stack and I/O addresses should also be in unpaged memory to make
them accessible from any page.
The starting address of a service routine must be located in unpaged memory because the 16-bit exception
vectors cannot point to addresses in paged memory. However, a service routine can call other routines that
are in paged memory. The upper 16K byte block of memory space (0xC000–0xFFFF) is unpaged. It is
recommended that all reset and interrupt vectors point to locations in this area.
3.4.3.1
CALL and RTC are uninterruptable instructions that automate page switching in the program expansion
window. CALL is similar to a JSR instruction, but the subroutine that is called can be located anywhere in
the normal 64K byte address space or on any page of program expansion memory. CALL calculates and
stacks a return address, stacks the current PPAGE value, and writes a new instruction-supplied value to
PPAGE. The PPAGE value controls which of the 64 possible pages is visible through the 16K byte
expansion window in the 64K byte memory map. Execution then begins at the address of the called
subroutine.
During the execution of a CALL instruction, the CPU:
This sequence is uninterruptable; there is no need to inhibit interrupts during CALL execution. A CALL
can be performed from any address in memory to any other address.
The PPAGE value supplied by the instruction is part of the effective address. For all addressing mode
variations except indexed-indirect modes, the new page value is provided by an immediate operand in the
instruction. In indexed-indirect variations of CALL, a pointer specifies memory locations where the new
page value and the address of the called subroutine are stored. Using indirect addressing for both the new
page value and the address within the page allows values calculated at run time rather than immediate
values that must be known at the time of assembly.
The RTC instruction terminates subroutines invoked by a CALL instruction. RTC unstacks the PPAGE
value and the return address and refills the queue. Execution resumes with the next instruction after the
CALL.
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Writes the old PPAGE value into an internal temporary register and writes the new instruction-
supplied PPAGE value into the PPAGE register.
Calculates the address of the next instruction after the CALL instruction (the return address), and
pushes this 16-bit value onto the stack.
Pushes the old PPAGE value onto the stack.
Calculates the effective address of the subroutine, refills the queue, and begins execution at the new
address on the selected page of the expansion window.
CALL and Return from Call Instructions
MC9S12C-Family / MC9S12GC-Family
Rev 01.23
Chapter 3 Module Mapping Control (MMCV4) Block Description
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