MC68020 Motorola, MC68020 Datasheet - Page 139

• Manufacturer Part Number: MC68020
• Description: (MC68020 / MC68EC020) MICROPROCESSORS USERS MANUAL
• Manufacturer: Motorola

level 6 interrupt is not processed. However, if the MC68020/EC020 is handling a level 7
interrupt (I2–I0 in the SR set to 111) and the external request is lowered to level 3 and
then raised back to level 7, a second level 7 interrupt is processed. The second level 7
interrupt is processed because the level 7 interrupt is transition sensitive. A level 7
interrupt is also generated by a level comparison if the request level and mask level are at
7 and the priority mask is then set to a lower level (with the MOVE to SR or RTE
instruction, for example). As shown in Figure 6-3 for level 6 interrupt request level and
mask level, this is the case for all interrupt levels.
Note that a mask value of 6 and a mask value of 7 both inhibit request levels of 1–6 from
being recognized. In addition, neither masks a transition to an interrupt request level of 7.
The only difference between mask values of 6 and 7 occurs when the interrupt request
level is 7 and the mask value is 7. If the mask value is lowered to 6, a second level 7
interrupt is recognized.
6-14
LEVEL 6 EXAMPLE
LEVEL 7 EXAMPLE
IF
IF
IF
IF STILL
IF
IF
IF
IF STILL
EXTERNAL IPL2–IPL0
001 ($6)
100 ($3)
001 ($6)
001 ($6)
100 ($3)
100 ($3)
000 ($7)
100 ($3)
000 ($7)
000 ($7)
Figure 6-3. Interrupt Recognition Examples
THEN
AND STILL
AND STILL
AND RTE SO THAT
THEN
AND STILL
AND STILL
AND RTE SO THAT
INTERRUPT PRIORITY MASK (I2–I0 IN SR)
M68020 USER’S MANUAL
101 ($5)
110 ($6)
110 ($6)
110 ($6)
101 ($5)
101 ($5)
111 ($7)
111 ($7)
111 ($7)
101 ($5)
INITIAL CONDITIONS
INITIAL CONDITIONS
THEN
THEN
THEN
AND
THEN
AND
THEN
THEN
LEVEL 6 INTERRUPT
NO ACTION
NO ACTION
LEVEL 6 INTERRUPT (LEVEL COMPARISON)
LEVEL 7 INTERRUPT (LEVEL COMPARISON)
LEVEL 7 INTERRUPT
NO ACTION
NO ACTION
ACTION
(LEVEL COMPARISON)
(TRANSITION)
(TRANSITION)
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