ST16C454(1994) 查看數據表（PDF） - Exar Corporation

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ST16C454
(Rev.:1994)

QUAD UNIVERSAL ASYNCHRONOUS RECEIVER/TRANSMITTER (UART)

Exar Corporation 

ST16C454/68C454

SYMBOL DESCRIPTION

Symbol

-IRQ

-RESET

RESET

R/-W

VCC

VCC

XTAL1

XTAL2

Rev. 3.20

Pin

Signal

type

under R/-W.

Pin Description

15

O

Interrupt Request or Interrupt “A” - This function is associated with

the 68 mode only. In the 68 mode, interrupts from UART channels

A-D are WIRE-OR’ed” internally to function as a single IRQ

interrupt. This pin transitions to a logic 0 (if enabled by the interrupt

enable register) whenever a UART channel(s) requires service.

Individual channel interrupt status can be determined by address-

ing each channel through its associated internal register, using -

CS and A3-A4. In the 68 mode an external pull-up resistor must be

connected between this pin and VCC. The function of this pin

changes to INTA when operating in the 16 mode, see definition

under INTA.

37

18

13

47,64

35

36

I

Reset. - In the 16 mode a logic 1 on this pin will reset the internal

registers and all the outputs. The UART transmitter output and the

receiver input will be disabled during reset time. (See ST16C454

External Reset Conditions for initialization details.) When 16/-68

is a logic 0 (68 mode), this pin functions similarly but, as an inverted

reset interface signal, -RESET.

I

Read/Write Strobe (active low) - This function is associated with

the 68 mode only. This pin provides the combined functions for

Read or Write strobes. A logic 1 to 0 transition transfers the

contents of the CPU data bus (D0-D7) to the register selected by

-CS and A0-A4. Similarly a logic 0 to 1 transition places the

contents of a 454 register selected by -CS and A0-A4 on the data

bus, D0-D7, for transfer to an external CPU.

I

Power supply inputs.

I

Crystal or External Clock Input - Functions as a crystal input or as

an external clock input. A crystal can be connected between this

pin and XTAL2 to form an internal oscillator circuit (see figure 8).

Alternatively, an external clock can be connected to this pin to

provide custom data rates (see Baud Rate Generator Program-

ming).

O

Output of the Crystal Oscillator or Buffered Clock - (See also

XTAL1). Crystal oscillator output or buffered clock output.

6

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