MC68000 MOTOROLA [Motorola, Inc], MC68000 Datasheet - Page 76

• Manufacturer Part Number: MC68000
• Manufacturer: MOTOROLA [Motorola, Inc]

System Integration Block (SIB)
V7–V5—Interrupt Vector Bits 7–5
Bits 11 and 4–0—Reserved for future use.
3.2.5.2 Interrupt Pending Register (IPR)
Each bit in the 16-bit IPR corresponds to an INRQ interrupt source. When an INRQ interrupt
is received, the interrupt controller sets the corresponding bit in the IPR.
In a vectored interrupt environment, the interrupt controller clears the IPR bit when the vec-
tor number corresponding to the INRQ interrupt source is passed to the M68000 core during
an interrupt acknowledge cycle, unless an event register exists for that INRQ interrupt. In a
polled interrupt scheme, the user must periodically read the IPR. When a pending interrupt
is handled, the user should clear the corresponding bit in the IPR by writing a one to that bit.
(If an event register exists, the unmasked event register bits should be cleared instead,
causing the IPR bit to be cleared.) Since the user can only clear bits in this register, the bits
that are written as zeros will not be affected. The IPR is cleared at reset.
3-26
These three bits are concatenated with five bits provided by the interrupt controller, which
indicate the specific interrupt source, to form an 8-bit interrupt vector number. If these bits
are not written, the vector $0F is provided.
PB11
1 = Edge-triggered. An interrupt is made pending when IRQ1 changes from one to
PB9
15
7
zero (falling edge).
While in disable CPU mode, during the host processor interrupt
acknowledge cycle for IRQ1, if IRQ1 is not continuously assert-
ed, the interrupt controller will still provide the vector number
(and DTACK) according to the IV1 bit. The IACK6 falling edge
can be used externally to negate IRQ1.
These three bits should be greater than or equal to ‘010’ in order
to put the interrupt vector in the area of the exception vector ta-
ble for user vectors.
The ERR bit is set if the user drives the IPL2–IPL0 lines to inter-
rupt level 4 and no INRQ interrupt is pending.
TIMER2
PB10
14
6
SCC1
SCP
13
5
MC68302 USER’S MANUAL
TIMER3
SDMA
12
4
NOTE
NOTE
Note:
SMC1
IDMA
11
3
SMC2
SCC2
10
2
TIMER1
PB8
9
1
MOTOROLA
SCC3
ERR
8
0