Motorola 68HC12B32 Instrukcja Użytkownika Pobierz pdf (Strona 41)

OPERATION

68EVB912B32UM/D 3-19

CALL

Call Subroutine

CALL

syntax:

CALL [<Address>]

where:

<Address> is an optional 16-bit hexadecimal number.

The CALL command is used to execute a subroutine and return to the D-Bug12 monitor program

when the final RTS of the subroutine is executed. When control is returned to D-Bug12, the

CPU register contents are displayed. All CPU registers contain the values at the time the final

RTS instruction was executed, with the exception of the program counter (PC). The PC contains

the starting address of the subroutine. If a subroutine address is not supplied on the command

line, the current value of the Program Counter (PC) is used as the starting address.

NOTE:

No user breakpoints are placed in memory before execution is

transferred to user code.

restrictions:

If the called subroutine modifies the value of the stack pointer during its execution, it must

restore the stack pointer’s original value before executing the final RTS of the called subroutine.

This restriction is required because a return address is placed on the users stack that returns to

D-Bug12 when the final RTS of the subroutine is executed. Obviously, any subroutine must

obey this restriction to execute properly.

The CALL command cannot be issued when the "R>" prompt is displayed, indicating that the

target system is already running a user program.

example:

>CALL 820

Subroutine Call Returned

PC SP X Y D = A:B CCR = SXHI NZVC

0820 0A00 057C 0000 0F:F9 1001 0000

1 2 ... 36 37 38 39 40 41 42 43 44 45 46 ... 121 122

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Motorola 68HC12B32 Instrukcja Użytkownika Strona 41