XRT72L13 datasheet(199/370 Pages) EXAR

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XRT72L13

M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

PRELIMINARY

REV. P1.0.6

187

B.2

After some settling time, the data on the bi-

directional data bus will stabilize and can be

read by the µC/µP. The XRT72L13 DS3 Framer

will indicate that this data is ready to be read by

asserting the Rdy_Dtck (DTACK*) signal.

B.3

After the µC/µP detects the Rdy_Dtck signal

(from the XRT72L13 DS3 Framer), it terminates

the "Read" cycle by toggling the Rd_DS (Data

Strobe) input pin "high".

For subsequent read operations, within this burst cy-

cle, the µC/µP simply repeats steps B.1 through B.3,

as illustrated in Figure 56 .

3.2.2.2.2.1.3

Terminating the Burst Access

Operation

The Burst I/O Access will be terminated upon the fall-

ing edge of the ALE_AS input signal. At this point the

Framer will cease to internally increment the "latched"

address value. Further, the µC/µP is now free to exe-

cute either a "Programmed I/O" access or to start an-

other "Burst Access" Operation with the XRT72L13

DS3 Framer.

3.2.2.2.2.2

The "Motorola-Mode" Write Burst

Access

Whenever a "Motorola-type" µC/µP wishes to write

the contents of numerous registers or buffer locations

over a "contiguous" range of addresses, then it

should do the following.

a. Perform the initial "write" operation; of the burst

access.

b. Perform the remaining "write" operations, of the

burst access.

c. Terminate the burst access operation.

Each of these "operations" within the burst access

are described below.

3.2.2.2.2.2.1

The Initial Write Operation

The initial write operation of a "Motorola-type" Write

Burst Access is accomplished by executing a "Pro-

grammed I/O Write Cycle" as summarized below.

A.0

Execute a Single Ordinary (Programmed I/

O) Write cycle, as described in Steps A.1

through A.7 below.

A.1

Assert the ALE_AS (Address Strobe) input pin

by toggling it "low". This step enables the

Address Bus input drivers (within the

XRT72L13 DS3 Framer).

A.2

Place the address of the "initial" target register

or buffer location (within the Framer), on the

Address Bus input pins, A[8:0].

A.3

At the same time, the Address-Decoding cir-

cuitry (within the user's system) should assert

the CS* input pin of the Framer by toggling it

"low". This step enables further communication

between the µC/µP and the Framer Micropro-

cessor 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

FIGURE 56. BEHAVIOR THE MICROPROCESSOR INTERFACE SIGNALS, DURING SUBSEQUENT "READ" OPERATIONS

WITHIN THE

BURST I/O CYCLE (MOTOROLA-TYPE µC/µP)

ALE_AS

RDB_DS

A[8:0]

CS*

D[15:0]

Rdy_Dtck

Not Valid

Valid Data at Offset =0x01

WRB_RW

Not Valid

Valid Data at Offset =0x02

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

XRT72L13 Datasheet(PDF) 199 Page - Exar Corporation

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