CENTRAL PROCESSING UNIT (CPU)
2.1 Central processing unit
2–4
7751 Group User’s Manual
2.1.4 Stack pointer (S)
The stack pointer (S) is a 16-bit register. It is used for a subroutine call or an interrupt. It is also used when
addressing modes using the stack are executed. The contents of S indicate an address (stack area) for
storing registers during subroutine calls and interrupts. Bank 0
16
is specified for the stack area. (Refer to
“2.1.6 Program bank register (PG).”)
When an interrupt request is accepted, the microcomputer stores the contents of the program bank register
(PG) at the address indicated by the contents of S and decrements the contents of S by 1. Then the
contents of the program counter (PC) and the processor status register (PS) are stored. The contents of
S after accepting an interrupt request is equal to the contents of S decremented by 5 before the accepting
of the interrupt request. (Refer to Figure 2.1.2.)
When completing the process in the interrupt routine and returning to the original routine, the contents of
registers stored in the stack area are restored into the original registers in the reverse sequence (PS
→
PC
→
PG)
by executing the RTI instruction. The contents of S is returned to the state before accepting an interrupt
request.
The same operation is performed during a subroutine call, however, the contents of PS is not automatically
stored. (The contents of PG may not be stored. This depends on the addressing mode.)
The user should store registers other than those described above with software when the user needs them
during interrupts or subroutine calls.
Additionally, initialize S at the beginning of the program because its contents are undefined at reset. The
stack area changes when subroutines are nested or when multiple interrupt requests are accepted. Therefore,
make sure of the subroutine’s nesting depth not to destroy the necessary data.
Note: Refer to “7751 Series Software Manual” for addressing modes.
Fig. 2.1.2 Stored registers of the stack area
●
“S” is the initial address that the stack pointer (S)
indicates at accepting an interrupt request.
The S’s contents become “S–5” after storing the
above registers.
Address
S–4
S–3
S–2
S–1
S
Stack area
S–5
Processor status register’s low-order byte (PS
L
)
Processor status register’s high-order byte (PS
H
)
Program counter’s low-order byte (PC
L
)
Program counter’s high-order byte (PC
H
)
Program bank register (PG)
Summary of Contents for 7700 FAMILY
Page 2: ...MITSUBISHI 16 BIT SINGLE CHIP MICROCOMPUTER 7700 FAMILY 7751 SERIES 7751 Group User s Manual...
Page 11: ...Table of Contents viii 7751 Group User s Manual MEMORANDUM...
Page 157: ...TIMER B 6 28 7751 Group User s Manual 6 5 Pulse period pulse width measurement mode MEMORANDUM...
Page 245: ...7751 Group User s Manual 8 36 A D CONVERTER Precautions when using A D converter MEMORANDUM...
Page 265: ...7751 Group User s Manual WAIT MODE 11 6 11 3 Precautions for Wait mode MEMORANDUM...
Page 289: ...CONNECTION WITH EXTERNAL DEVICES 12 4 Hold function 7751 Group User s Manual 12 24 MEMORANDUM...
Page 290: ...CHAPTER 13 RESET 13 1 Hardware reset 13 2 Software reset...
Page 302: ...CHAPTER 14 CLOCK GENERATING CIRCUIT 14 1 Oscillation circuit example 14 2 Clock...
Page 307: ...CLOCK GENERATING CIRCUIT 7751 Group User s Manual 14 6 14 2 Clock MEMORANDUM...
Page 360: ...CHAPTER 16 STANDARD CHARACTERISTICS 16 1 Standard characteristics...
Page 366: ...CHAPTER 17 APPLICATIONS 17 1 Memory expansion...
Page 405: ...APPLICATIONS 7751 Group User s Manual 17 40 17 1 Memory expansion MEMORANDUM...
Page 406: ...CHAPTER 18 PROM VERSION 18 1 EPROM mode 18 2 Usage precaution...
Page 417: ...7751 Group User s Manual PROM VERSION 18 12 18 2 Usage precaution MEMORANDUM...
Page 418: ...CHAPTER 19 FLASH MEMORY VERSION 19 1 Parallel input output mode 19 2 Serial input output mode...
Page 451: ...FLASH MEMORY VERSION 7751 Group User s Manual 19 34 19 2 Serial input output mode MEMORANDUM...
Page 484: ...APPENDIX 7751 Group User s Manual 20 33 Appendix 4 Package outlines 80D0...
Page 489: ...APPENDIX 7751 Group User s Manual 20 38 Appendix 6 Hexadecimal instruction code table...
Page 490: ...APPENDIX 7751 Group User s Manual 20 39 Appendix 6 Hexadecimal instruction code table...
Page 492: ...APPENDIX 7751 Group User s Manual 20 41 Appendix 7 Machine instructions...
Page 493: ...APPENDIX 7751 Group User s Manual 20 42 Appendix 7 Machine instructions...
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Page 535: ...APPENDIX Appendix 9 Q A 7751 Group User s Manual 20 84 MEMORANDUM...
Page 536: ...GLOSSARY...
Page 539: ...GLOSSARY 7751 Group User s Manual 4 MEMORANDUM...