SPMC68CK338CPV14 datasheet(45/133 Pages) FREESCALE

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MC68CK338

MOTOROLA

MC68CK338TS/D

The CPU32L provides seven levels of interrupt priority (1–7), seven automatic interrupt vectors, and

200 assignable interrupt vectors. All interrupts with priorities less than seven can be masked by the in-

terrupt priority (IP) field in status register. The CPU32L handles interrupts as a type of asynchronous

expression.

There are seven interrupt request signals (IRQ[7:1]). These signals are used internally on the IMB, and

there are corresponding pins for external interrupt service requests. The CPU treats all interrupt re-

quests as though they come from internal modules — external interrupt requests are treated as interrupt

service requests from the SIML. Each of the interrupt request signals corresponds to an interrupt priority

level. IRQ1 has the lowest priority and IRQ7 the highest.

Interrupt recognition is determined by interrupt priority level and interrupt priority mask value. The inter-

rupt priority mask consists of three bits in the CPU32L status register. Binary values %000 to %111 pro-

vide eight priority masks. Masks prevent an interrupt request of a priority less than or equal to the mask

value from being recognized and processed. IRQ7, however, is always recognized, even if the mask

value is %111.

IRQ[7:1] are active-low level-sensitive inputs. The low on the pin must remain asserted until an interrupt

acknowledge cycle corresponding to that level is detected.

IRQ7 is transition-sensitive as well as level-sensitive: a level 7 interrupt is not detected unless a falling

edge transition is detected on the IRQ7 line. This prevents redundant servicing and stack overflow. A

non-maskable interrupt is generated each time IRQ7 is asserted as well as each time the priority mask

changes from %111 to a lower number while IRQ7 is asserted.

Interrupt requests are sampled on consecutive falling edges of the system clock. Interrupt request input

circuitry has hysteresis: to be valid, a request signal must be asserted for at least two consecutive clock

periods. Valid requests do not cause immediate exception processing, but are left pending. Pending re-

quests are processed at instruction boundaries or when exception processing of higher-priority excep-

tions is complete.

The CPU32L does not latch the priority of a pending interrupt request. If an interrupt source of higher

priority makes a service request while a lower priority request is pending, the higher priority request is

serviced. If an interrupt request with a priority equal to or lower than the current IP mask value is made,

the CPU32L does not recognize the occurrence of the request. If simultaneous interrupt requests of dif-

ferent priorities are made, and both have a priority greater than the mask value, the CPU32L recognizes

the higher-level request.

3.9.1 Interrupt Acknowledge and Arbitration

When the CPU32L detects one or more interrupt requests of a priority higher than the interrupt priority

mask value, it places the interrupt request level on the address bus and initiates a CPU space read cy-

cle. The request level serves two purposes: it is decoded by modules or external devices that have re-

quested interrupt service, to determine whether the current interrupt acknowledge cycle pertains to

them, and it is latched into the interrupt priority mask field in the CPU32L status register, to preclude

further interrupts of lower priority during interrupt service.

Modules or external devices that have requested interrupt service must decode the interrupt priority

mask value placed on the address bus during the interrupt acknowledge cycle and respond if the priority

of the service request corresponds to the mask value. However, before modules or external devices

respond, interrupt arbitration takes place.

Freescale Semiconductor, Inc.

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SPMC68CK338CPV14 Datasheet(PDF) 45 Page - Freescale Semiconductor, Inc

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