AM85C30 datasheet(8/68 Pages) AMD

8 / 68 page

AMD

Am85C30

W/REQA, W/REQB

Wait/Request (Outputs; Open drain when pro-

grammed for a Wait function, driven High or Low

when programmed for a Request function)

These dual-purpose outputs may be programmed as

Request lines for a DMA controller or as Wait lines to

synchronize the CPU to the SCC data rate. The reset

state is Wait.

Control

A/B

Channel A/Channel B Select (Input)

This signal selects the channel in which the Read or

Write operation occurs.

Chip Enable (Input; Active Low)

This signal selects the SCC for a Read or Write

operation.

D/C

Data/Control Select (Input)

This signal defines the type of information transferred to

or from the SCC. A High means data is transferred; a

Low indicates a command is transferred.

Data Bus

D7–D0

Data Bus (Input/Output; Three State)

These lines carry data and commands to and from the

SCC.

Interrupt

IEI

Interrupt Enable In (Input; Active High)

IEI is used with IEO to form an interrupt daisy chain

when there is more than one interrupt-driven device. A

High IEI indicates that no other higher priority device has

an interrupt under service or is requesting an interrupt.

IEO

Interrupt Enable Out (Output; Active High)

IEO is High only if IEI is High and the CPU is not servic-

ing an SCC interrupt or the SCC is not requesting an

interrupt (interrupt acknowledge cycle only). IEO is con-

nected to the next lower priority device’s IEI input and

thus inhibits interrupts from lower priority devices.

INT

Interrupt Request (Output; Active Low,

Open Drain)

This signal is activated when the SCC requests an

interrupt.

INTACK

Interrupt Acknowledge (Input; Active Low)

This signal indicates an active interrupt acknowledge

cycle. During this cycle, the SCC interrupt daisy chain

settles. When

RD becomes active, the SCC places an

interrupt vector on the data bus (if IEI is High).

INTACK

is latched by the rising edge of PCLK.

Serial Data

RxDA, RxDB

Receive Data (Inputs; Active High)

These input signals receive serial data at standard TTL

levels.

TxDA, TxDB

Transmit Data (Outputs; Active High)

These output signals transmit serial data at standard

TTL levels.

Miscellaneous

GND

Ground

PCLK

Clock (Input)

This is the master SCC clock used to synchronize inter-

nal signals. PCLK is not required to have any phase

relationship with the master system clock. PCLK is a

TTL- level signal. Maximum transmit rate is 1/4 PCLK.

VCC

+ 5 V Power Supply

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