XRT7250 datasheet(69/463 Pages) EXAR

69 / 463 page

XRT7250

DS3/E3 FRAMER IC

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REV. 1.1.1

tion between the µC/µP and the Framer Micro-

processor Interface block.

A.4

After allowing the data on the Address Bus pins

to settle (by waiting the appropriate Address

Setup time), the µC/µP should toggle the

ALE_AS input pin "High". This step causes the

Framer device to latch the contents of the

Address Bus into its own circuitry. At this point,

the initial address of the burst access has now

been selected.

A.5

Further, the µC/µP should indicate that this cur-

rent bus cycle is a Write operation by toggling

the WR_RW (R/W*) input pin "Low".

A.6

The µC/µP should then place the byte or word

that it intends to write into the target register, on

the bi-directional data bus, D[7:0].

A.7

Next, the µC/µP should initiate the bus cycle by

toggling the RD_DS (Data Strobe) input pin

"Low". When the XRT7250 DS3/E3 Framer

device senses that the WR_RW input pin is

"Low", and that the RD_DS input pin has tog-

gled "Low" it will enable the input drivers of the

bi-directional data bus, D[7:0].

A.8

After waiting the appropriate amount of time, for

this newly placed data to settle on the bi-direc-

tional data bus (e.g., the Data Setup time) the

Framer will assert the RDY_DTCK (DTACK)

output signal.

A.9

After the µP/µC detects the RDY_DTCK signal

(from the Framer) it should toggle the RD_DS

input pin "High". This action accomplishes two

things:

a. It latches the contents of the bi-directional data

bus into the XRT7250 DS3/E3 Framer Micropro-

cessor Interface block.

b. It terminates the Write cycle.

Figure 35 presents a timing diagram which illustrates

the behavior of the Microprocessor Interface signals,

during the Initial write operation within a Burst Ac-

cess, for a Motorola-type µC/µP.

At the completion of this initial write cycle, the µC/µP

has written a byte or word into the first register or

buffer location (within the XRT7250 DS3/E3 Framer)

for this particular burst I/O access. In order to illus-

trate how this burst I/O cycle works, the byte (or word)

of data, that is being written in Figure 35 has been la-

beled Data to be Written (Offset = 0x00).

2.2.2.2.2.2.2

The Subsequent Write Operations

The procedure that the µC/µP must use to perform

the remaining write cycles, within this burst access

operation, is presented below.

B.0

Execute each subsequent write cycle, as

described in Steps B.1 through B.3

B.1

Without toggling the ALE_AS (Address Strobe)

input pin (e.g., keeping it "High"), apply the

value of the next byte or word (to be written into

the Framer) to the bi-directional data bus pins,

D[7:0].

B.2

Toggle the RD_DS (Data Strobe) input pin

"Low". This step accomplishes the following.

a. The Framer internally increments the latched

address value (within the Microprocessor Inter-

face).

FIGURE 35. BEHAVIOR OF THE MICROPROCESSOR INTERFACE SIGNALS, DURING THE INITIAL WRITE OPERATION OF

BURST CYCLE (MOTOROLA-TYPE PROCESSOR)

ALE_AS

A[8:0]

D[15:0]

RD_DS

RDY_DTCK

Data to be Written (Offset = 0x00)

Address of “Initial” Target Register (Offset = 0x00)

WR_RW

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