Motorola M68000 Betriebsanweisung Seite 185

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Exception Processing, System Control Operations, and I/O 171
13. What exception vectors are associated with the TRAP instruction?
14. Is an exception generated for an overflow condition?
15. What happens if the trace bit is set in the status register?
16. Does the 68000 restrict the user to specific instructions for I/O?
17. What is the difference between a serial and a parallel interface?
18. What is the purpose of a parity bit?
19. What two methods can be used to program the 6850 ACIA?
20. What is the purpose of the MOVEP instruction?
21. What instruction is normally used as a place holder?
22. After the STOP instruction has been executed, is it possible for the
CPU to start up again?
23. What instruction is used in a multi-processor system for locking op
erations?
Answers
1. Two bytes.
2. The 3-bit interrupt mask, the supervisor state bit, and the trace mode
bit.
3. It can be read but not written using the MOVE from SR instruction.
4. The interrupt mask can range from 0 through 7.
5. ANDi #$f e ,s r
6. The RTR instruction is used to restore the saved CCR bits from the
stack and return. It allows the writing of a transparent subroutine.
7. SMI MINUS
8. l e a u s t a c k ,a o
MOVE A 0 fUSP
9. An event that causes the normal flow of a program to be suspended,
and control given to a special handler.
10. In memory, starting at location zero, for a total of 1024 bytes.
11. The RTE is used to return from an exception. The SR as well as the return
address are popped from the stack. The RTS is used to return from a
subroutine and only the return address is popped from the stack.
12. The address error exception is generated.
13. Vector numbers 32 through 47.
14. No, but the TRAPV instruction can be used to generate one.
15. An exception is generated after every instruction execution. Vector
number 9 is used.
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