XRT7250 datasheet(22/463 Pages) EXAR

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DS3/E3 FRAMER IC

XRT7250

REV. 1.1.1

PIN DESCRIPTIONS

PIN DESCRIPTION

PIN #NAME

TYPE

DESCRIPTION

Not Bonded Out

VDD

****

Power Supply Pin

Not Bonded Out

GND

****

Ground Pin

Rdy_Dtck

READY or DTACK

This active-low output pin will function as the READY output, when the micro-

processor interface is running in the "Intel" Mode; and will function as the

DTACK output, when the microprocessor interface is running in the "Motorola"

Mode.

"Intel" Mode - READY Output

When the Framer negates this output pin (e.g., toggles it "low"), it indicates (to

the µP) that the current READ or WRITE cycle is to be extended until this sig-

nal is asserted (e.g., toggled "high").

"Motorola" Mode - DTACK (Data Transfer Acknowledge) Output

The Framer device will assert this pin in order to inform the local microproces-

sor that the present READ or WRITE cycle is nearly complete. If the Framer

device requires that the current READ or WRITE cycle be extended, then the

Framer will delay its assertion of this signal. The 68000 family of µPs requires

this signal from its peripheral devices, in order to quickly and properly complete

a READ or WRITE cycle.

WR_RW

Write Data Strobe (Intel Mode)

If the microprocessor interface is operating in the Intel Mode, then this active-

low input pin functions as the WR (Write Strobe) input signal from the µP. Once

this active-low signal is asserted, then the Framer will latch the contents of the

µP Data Bus, into the addressed register (or RAM location) within the Framer

IC. In the Intel Mode, data gets latched on the rising edge of WR

R/W Input Pin (Motorola Mode)

When the Microprocessor Interface Section is operating in the Motorola Mode,

then this pin is functionally equivalent to the R/W pin. In the Motorola Mode, a

READ operation occurs if this pin is at a logic "1". Similarly, a WRITE operation

occurs if this pin is at a logic "0".

Chip Select Input

This active-low input signal selects the Microprocessor Interface Section of the

Framer device and enables READ/WRITE operations between the Local

Microprocessor and the Framer on-chip registers and RAM locations.

ALE_AS

Address Latch Enable/Address Strobe

This input is used to latch the address (present at the Microprocessor Interface

Address Bus, A[8:0]) into the Framer Microprocessor Interface circuitry and to

indicate the start of a READ/WRITE cycle. This input is active-high in the Intel

Mode (MOTO = "low") and active-low in the Motorola Mode (MOTO = "high").

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