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MS7200L/7201AL/7202AL

MOSEL VITELIC

MS7200L/01AL/02AL Rev. 1.0 January 1995

Signal Descriptions

INPUTS:

These data inputs accept 9-bit data words for

sequential storage in the FIFO during write

operations.

CONTROLS:

Reset (

RS)

The reset input is active LOW. When asserted,

the device is asynchronously reset, and both the

read and write internal pointers are set to the first

location in the FIFO. A Reset is required after

power-up before a write operation can occur. Both

Read Enable (

R) and Write Enable (W) must be

HIGH during Reset.

Read Enable (

R)

The read enable input is active LOW. As long as

the Empty Flag (

EF) is not set, the read cycle is

started on the falling edge of this signal. The data is

accessed on a First-In/First-Out basis, independent

of any write activity, and is presented on the Data

Output pins (Q0 - Q8). When

R goes HIGH the Data

Output pins return to the high impedance state, and

the read pointer is incremented. When the FIFO is

empty or all of the data has been read, the Empty

Flag will be set and further read operations are

inhibited until a valid write operation has been

performed.

Write Enable (

W)

The write enable input is active LOW. As long as

the Full Flag (

FF) is not set, the write cycle is started

on the falling edge of this signal. The data present

on the Data Input pins (D0 - D8) is stored

sequentially, independent of any read activity.

When

W goes HIGH the write cycle is terminated

and the write pointer is incremented. When the

maximum capacity of the FIFO has been reached

the Full Flag will be set, and further write operations

are inhibited until a valid read operation has been

performed.

Expansion In (

XI)

This input pin serves two purposes. When

grounded, it indicates that the device is being

operated in the single device mode. In Depth

Expansion mode, this pin is connected to the

Expansion Out Output (

XO) of the previous device.

First Load/Retransmit (

FL/RT)

This is a dual-purpose input. In single device

mode (when Expansion In (

XI) is grounded) this pin

acts as the retransmit input. A LOW pulse on this

will reset the read pointer to the first memory

location of the FIFO. The write pointer is unaffected.

Both the read enable (

R) and write enable (W)

inputs must remain HIGH during the retransmit

cycle.

In Depth Expansion mode this pin acts as a first

load indicator. It must be grounded on the first

device in the chain to indicate which device is the

first to receive data.

OUTPUTS:

A 9 bit data word from the FIFO is output on these

pins during read operations. They are in the high

impedance state whenever

R is HIGH.

Empty Flag (

EF)

This output is active LOW. When all of the data

has been read from the FIFO (defined as when the

Read pointer is one location behind the Write

pointer) this flag will be set. The Data Output pins

will be forced into the high impedance state, and all

further read operations will be inhibited until a valid

write operation has been performed (which will

reset this flag).

Full Flag (

FF)

This output is active LOW. To prevent data

overflow, when the maximum capacity of the FIFO

has been reached (defined as when the Write

pointer is one location behind the Read pointer) this

flag will be set. All further write operations will be

inhibited until a valid read operation has been

performed (which will reset this flag).

Expansion Out/Half Full Flag (

XO/HF)

This dual-purpose output is active LOW. In single

device mode (when Expansion In (

XI) is grounded)

this flag will be set at the falling edge of the next

write operation after the FIFO has reached one-half

of its maximum capacity. This flag will remain set as

long as the difference between the read pointer and

the write pointer is greater than one-half of the

maximum capacity of the FIFO.

In Depth Expansion mode, this output is

connected to the Expansion In Input of the next

device in the chain. The Expansion Out pin

provides a pulse to the next device in the chain

when the last memory location has been reached.