AM186ED-20KCSLASHW datasheet(23/88 Pages) AMD

23 / 88 page

Am186ED/EDLV Microcontrollers

PRELI M INARY

F T

port 0 control register is set). The ENRX0 signal

enables the receiver for the associated serial port.

DEN/DS/PIO5

Data Enable (output, three-state, synchronous)

Data Strobe (output, three-state, synchronous)

DEN—This pin supplies an output enable to an

external data-bus transceiver. DEN is asserted during

memory, I/O, and interrupt acknowledge cycles. DEN is

deasserted when DT/R changes state. DEN floats

during a bus hold or reset condition.

DS—The data strobe provides a signal where the write

cycle timing is identical to the read cycle timing. When

used with other control signals, DS provides an

interface for 68K-type peripherals without the need for

additional system interface logic.

When DS is asserted, addresses are valid. When DS is

asserted on writes, data is valid. When DS is asserted

on reads, data can be asserted on the AD bus.

Note: This pin resets to DEN.

DRQ0/INT5/PIO12

DMA Request 0 (input, synchronous,

level-sensitive)

Maskable Interrupt Request 5 (input,

asynchronous, edge-triggered)

DRQ0—This pin indicates to the microcontroller that an

external device is ready for DMA channel 0 to perform

a transfer. DRQ0 is level-triggered and internally

synchronized. DRQ0 is not latched and must remain

active until serviced.

INT5—If DMA 0 is not enabled or DMA 0 is not being

used with external synchronization, INT5 can be used

as an additional external interrupt request. INT5 shares

the DMA 0 interrupt type (0Ah) and register control bits.

INT5 is edge-triggered only and must be held until the

interrupt is acknowledged.

DRQ1/INT6/PIO13

DMA Request 1 (input, synchronous,

level-sensitive)

Maskable Interrupt Request 6 (input,

asynchronous, edge-triggered)

DRQ1—This pin indicates to the microcontroller that an

external device is ready for DMA channel 1 to perform

a transfer. DRQ1 is level-triggered and internally

synchronized. DRQ1 is not latched and must remain

active until serviced.

INT6—If DMA 1 is not enabled or DMA 1 is not being

used with external synchronization, INT6 can be used

as an additional external interrupt request. INT6 shares

the DMA 1 interrupt type (0Bh) and register control bits.

INT6 is edge-triggered only and must be held until the

interrupt is acknowledged.

DT/R/PIO4

Data Transmit or Receive (output, three-state,

synchronous)

This pin indicates in which direction data should flow

through an external data-bus transceiver. When DT/R

is asserted High, the microcontroller transmits data.

When this pin is deasserted Low, the microcontroller

receives data. DT/R floats during a bus hold or reset

condition.

GND

Ground

Ground pins connect the microcontroller to the system

ground.

HLDA

Bus Hold Acknowledge (output, synchronous)

This pin is asserted High to indicate to an external bus

master that the microcontroller has released control of

the local bus. When an external bus master requests

control of the local bus (by asserting HOLD), the

microcontroller completes the bus cycle in progress. It

then relinquishes control of the bus to the external bus

master by asserting HLDA and floating DEN, RD, WR,

S2–S0, AD15–AD0, S6, A19–A0, BHE, WHB, WLB,

and DT/R. The following chip selects are three-stated

(then will be held High with an ~10-kohm resistor):

UCS, LCS, MCS3–MCS0, PCS6–PCS5, PCS3–PCS0,

RAS0, RAS1, UCAS, and LCAS. ALE is also three-

stated (then will be held Low with an ~10-kohm

resistor).

When the external bus master has finished using the

local bus, it indicates this to the microcontroller by

deasserting HOLD. The microcontroller responds by

deasserting HLDA.

If the microcontroller requires access to the bus (for

example, to refresh), it will deassert HLDA before the

external bus master deasserts HOLD. The external bus

master must be able to deassert HOLD and allow the

microcontroller access to the bus. See the timing

diagrams for bus hold on page 86.

HOLD

Bus Hold Request (input, synchronous,

level-sensitive)

This pin indicates to the microcontroller that an external

bus master needs control of the local bus.

The Am186ED/EDLV microcontrollers’ HOLD latency

time, that is, the time between HOLD request and

HOLD acknowledge, is a function of the activity occur-

ring in the processor when the HOLD request is re-

ceived. A HOLD request is second only to DRAM

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