CPU Description
Call Native Routine (CALLN)
The CALLN instruction makes it possible to call native mode
subroutines when in emulation mode. The processing steps taken by
this instruction are similar in 8080 code to those taken by the BRK
[INT] instruction in 8088/8086 code. The 8-bit immediate operand of
this instruction specifies an interrupt vector type, which is then
multiplied (shifted left 2 bits) by four to create an address. This
address holds the program code segment (PS) and offset (PC) of the
native mode subroutine.
The contents of the PSW, PS, and PC [IF, CS, and IP] are pushed onto
the stack, saving the MD bit in the PSW on the stack as 0. Then the
MD bit is set to a logical 1 in the PSW [FL], and the contents of the
PS and PC [CS and IP] are loaded with the new segment and offset
address of the native mode subroutine.
Return from Interrupt (RETI)
This is a general purpose instruction used to return from a native
mode interrupt service routine entered by the BRK [INT] instruction
or by an external interrupt. This instruction is also used to return from
a native mode subroutine entered by the CALLN instruction.
Restoration of the PSW, PS, and PC [IF, CS, and IP] from the top of
the stack is done exactly the same as the native mode execution. The
restored PSW determines the mode in which the processor will
execute. If returning to the emulation mode, as from a routine called
by CALLN, then the MD is a logical 1, signifying emulation mode.
6-15
Содержание ZT 8809A
Страница 15: ...Tables Table B 9 J5 Pin Assignments B 17 Table B 10 J6 Pin Assignments B 18 Table B 11 J7 Pin Assignments B 19...
Страница 334: ...Jumper Configurations W49 W48 A W47 B A B W37 W66 A W50 B C J7 W67 Figure A 11 W37 W47 50 W66 W67 Jumper Blocks A 34...
Страница 346: ...Jumper Configurations W61 W60 W62 W63 W64 A B A B W65 Figure A 13 W60 W65 Jumper Block A 46...