DEMO9S08EL32 Freescale Semiconductor, DEMO9S08EL32 Datasheet - Page 66

• Manufacturer Part Number: DEMO9S08EL32
• Description: BOARD DEMO FOR 9S08 EL MCU
• Manufacturer: Freescale Semiconductor
• Type: MCUr

Specifications of DEMO9S08EL32

• Contents: Evaluation Board
• Processor To Be Evaluated: MC9S08EL32
• Data Bus Width: 8 bit
• Interface Type: RS-232, USB
• Operating Supply Voltage: 12 V
• Silicon Manufacturer: Freescale
• Core Architecture: HCS08
• Core Sub-architecture: HCS08
• Silicon Core Number: MC9S08
• Silicon Family Name: S08EL
• Rohs Compliant: Yes
• For Use With/related Products: MC9S08EL32
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Chapter 5 Resets, Interrupts, and General System Control
recommended for anyone other than the most experienced programmers because it can lead to subtle
program errors that are difficult to debug.
The interrupt service routine ends with a return-from-interrupt (RTI) instruction which restores the CCR,
A, X, and PC registers to their pre-interrupt values by reading the previously saved information from the
stack.
If more than one interrupt is pending when the I bit is cleared, the highest priority source is serviced first
(see
5.5.1
Figure 5-1
(SP) points at the next available byte location on the stack. The current values of CPU registers are stored
on the stack starting with the low-order byte of the program counter (PCL) and ending with the CCR. After
stacking, the SP points at the next available location on the stack which is the address that is one less than
the address where the CCR was saved. The PC value that is stacked is the address of the instruction in the
main program that would have executed next if the interrupt had not occurred.
When an RTI instruction is executed, these values are recovered from the stack in reverse order. As part
of the RTI sequence, the CPU fills the instruction pipeline by reading three bytes of program information,
starting from the PC address recovered from the stack.
66
Table
5-2).
shows the contents and organization of a stack frame. Before the interrupt, the stack pointer
Interrupt Stack Frame
For compatibility with M68HC08 devices, the H register is not
automatically saved and restored. It is good programming practice to push
H onto the stack at the start of the interrupt service routine (ISR) and restore
it immediately before the RTI that is used to return from the ISR.
MC9S08EL32 Series and MC9S08SL16 Series Data Sheet, Rev. 3
STACKING
ORDER
UNSTACKING
5
4
3
2
1
ORDER
1
2
3
4
5
Figure 5-1. Interrupt Stack Frame
* High byte (H) of index register is not automatically stacked.
7
INDEX REGISTER (LOW BYTE X)
CONDITION CODE REGISTER
PROGRAM COUNTER HIGH
PROGRAM COUNTER LOW
ACCUMULATOR
NOTE
²
²
²
²
TOWARD HIGHER ADDRESSES
TOWARD LOWER ADDRESSES
*
0
SP AFTER
INTERRUPT STACKING
SP BEFORE
THE INTERRUPT
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