Make your own free website on Tripod.com

RETN

Return from non-maskable interrupt.
Function: PClow <- (SP); PChigh <- (SP + 1); SP <- SP + 2; IFF1 <- IFF2
 
Format:
1110 1101
 
byte 1: ED
 
0100 0101
 
byte 2: 45
 
Description: The program counter is popped off the stack as described for the POP instructions. Then the contents of the IFF2 (storage flip-flop) is copied back into the IFF1 to restore the state of the interrupt flag before the non-maskable interrupt.
 
Data Flow:
 
Timing: 4 M cycles; 14 T states: 7 usec @ 2 MHz
 
Addressing Mode: indirect
 
Flags:
 
(no effect)
 
Example:
RETN

OBJECT CODE
Before:
 
After: