MC68331MFC16 datasheet(34/84 Pages) FREESCALE

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MC68331TS/D

SPACE —Address Space

Use this option field to select an address space for the chip-select logic. The CPU32 normally operates

in supervisor or user space, but interrupt acknowledge cycles must take place in CPU space.

IPL —Interrupt Priority Level

If the space field is set for CPU space (00), chip-select logic can be used for interrupt acknowledge.

During an interrupt acknowledge cycle, the priority level on address lines ADDR[3:1] is compared to the

value in the IPL field. If the values are the same, a chip select is asserted, provided that other option

This field only affects the response of chip selects and does not affect interrupt recognition by the CPU.

Any level means that chip select is asserted regardless of the level of the interrupt acknowledge cycle.

AVEC —Autovector Enable

0 = External interrupt vector enabled

1 = Autovector enabled

This field selects one of two methods of acquiring the interrupt vector during the interrupt acknowledge

cycle. It is not usually used in conjunction with a chip-select pin.

If the chip select is configured to trigger on an interrupt acknowledge cycle (SPACE = 00) and the AVEC

field is set to one, the chip select automatically generates an AVEC in response to the interrupt cycle.

Otherwise, the vector must be supplied by the requesting device.

The AVEC bit must not be used in synchronous mode, as autovector response timing can vary because

of ECLK synchronization.

3.5.5 Port C Data Register

Bit values in port C determine the state of chip-select pins used for discrete output. When a pin is as-

signed as a discrete output, the value in this register appears at the output. This is a read/write register.

Bit 7 is not used. Writing to this bit has no effect, and it always returns zero when read.

Space Field

Address Space

CPU Space

User Space

Supervisor Space

Supervisor/User Space

IPL

Description

000

Any Level

001

IPL1

010

IPL2

011

IPL3

100

IPL4

101

IPL5

110

IPL6

111

IPL7

PORTC — Port C Data Register

$YFFA41

NOT USED

PC6

PC5

PC4

PC3

PC2

PC1

PC0

RESET:

Freescale Semiconductor, Inc.

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