Typewriter User Manual

2- 6 MC68340 USER’S MANUAL MOTOROLA

Port B4, B2, B1, AVEC

This signal group functions as three bits of parallel I/O and the autovector input. AVEC

requests an automatic vector during an interrupt acknowledge cycle.

2.6 INTERRUPT REQUEST LEVEL (IRQ7, IRQ6, IRQ5, IRQ3)

These pins can be programmed to be either prioritized interrupt request lines or port B

parallel I/O.

IRQ7, IRQ6, IRQ5, IRQ3

IRQ7

, the highest priority, is nonmaskable. IRQ6–IRQ1 are internally maskable

interrupts. Refer to Section 5 CPU32 for more information on interrupt request lines.

Port B7, B6, B5, B3

These pins can be used as port B parallel I/O. Refer to Section 4 System Integration

Module for more information on parallel I/O signals.

2.7 BUS CONTROL SIGNALS

These signals control the bus transfer operations of the MC68340. Refer to Section 3

Bus Operation for more information on these signals.

2.7.1 Data and Size Acknowledge (DSACK1, DSACK0)

These two active-low input signals allow asynchronous data transfers and dynamic data

bus sizing between the MC68340 and external devices as listed in Table 2-3. During bus

cycles, external devices assert

DSACK1 and/or DSACK0 as part of the bus protocol.

During a read cycle, this signals the MC68340 to terminate the bus cycle and to latch the

data. During a write cycle, this indicates that the external device has successfully stored

the data and that the cycle may terminate.

Table 2-3.

DSACK≈ Encoding

DSACK

Result

1 1 Insert Wait States in Current Bus Cycle

1 0 Complete Cycle—Data Bus Port Size Is 8 Bits

0 1 Complete Cycle—Data Bus Port Size Is 16 Bits

0 0 Reserved—Defaults to 16-Bit Port Size Can Be

Used for 32-Bit DMA Cycles

2.7.2 Address Strobe (AS)

AS is an output timing signal that indicates the validity of both an address on the address

bus and many control signals.

AS is asserted approximately one-half clock cycle after the

beginning of a bus cycle.

Frees

cale Semiconductor,

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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