Intel 8XC196NP, 80C196NU, Microcontroller manual CPU Special-function Registers SFRs, CPU SFRs

8XC196NP, 80C196NU USER’S MANUAL

Subroutines may be nested. That is, each subroutine may call other subroutines. The CPU PUSH- es the contents of the program counter onto the stack each time it executes a subroutine call. The stack grows downward as entries are added. The only limit to the nesting depth is the amount of available memory. As the CPU returns from each nested subroutine, it POPs the address off the top of the stack, and the next return address moves to the top of the stack.

Your program must load a word-aligned (even) address into the stack pointer. Select an address that is two bytes (for 64-Kbyte mode) or four bytes (for 1-Mbyte mode) greater than the desired starting address because the CPU automatically decrements the stack pointer before it pushes the first byte of the return address onto the stack. Remember that the stack grows downward, so allow sufficient room for the maximum number of stack entries. The stack must be located in page 00H, in either the internal register file or external RAM. The stack can be used most efficiently when it is located in the upper register file.

The following example initializes the top of the upper register file as the stack.

LD SP, #400H ;Load stack pointer

5.2.4.3CPU Special-function Registers (SFRs)

Locations 0000–0017H in the lower register file are the CPU SFRs. Table 5-7 lists the CPU SFRs for the 8XC196NP and the 80C196NU and highlights those that are unique to the 80C196NU. Appendix C describes the CPU SFRs.

Table 5-7. CPU SFRs

8XC196NP CPU SFRs

Address	High (Odd) Byte	Low (Even) Byte
0016H	Reserved	Reserved
0014H	Reserved	WSR
0012H	INT_MASK1	INT_PEND1
0010H	Reserved	Reserved
000EH	Reserved	Reserved
000CH	Reserved	Reserved
000AH	Reserved	Reserved
0008H	INT_PEND	INT_MASK
0006H	PTSSRV (H)	PTSSRV (L)
0004H	PTSSEL (H)	PTSSEL (L)
0002H	ONES_REG (H)	ONES_REG (L)
0000H	ZERO_REG (H)	ZERO_REG (L)

†These SFRs are unique to the 80C196NU.

††Must be addressed as a word.

80C196NU CPU SFRs

Address	High (Odd) Byte	Low (Even) Byte
0016H	Reserved	Reserved
0014H	WSR1†	WSR
0012H	INT_MASK1	INT_PEND1
0010H	Reserved	Reserved
000EH††	ACC_03†	ACC_02†
000CH††	ACC_01†	ACC_00†
000AH	ACC_STAT†	Reserved
0008H	INT_PEND	INT_MASK
0006H	PTSSRV (H)	PTSSRV (L)
0004H	PTSSEL (H)	PTSSEL (L)
0002H	ONES_REG (H)	ONES_REG (L)
0000H	ZERO_REG (H)	ZERO_REG (L)

5-12