Philips Semiconductors

Product specification

74F225

16

× 5 asynchronous FIFO (3-State)

2

June 15, 1992

853-1652 06992

FEATURES

DESCRIPTION

This 80–bit active element First–In–First–Out (FIFO) is a monolithic

Schottky–clamped transistor–transistor logic (STTL) array organized

as 16–words of 5–bits each. A memory system using the ’F225 can

be easily expanded in multiples of 16–words of 5–bits as shown in

Figure 1. The 3–State outputs controlled by a single enable input

(OE) make bus connection and multiplexing simple. The ’F225

processes data in a parallel format at any desired clock rate from

DC to 25MHz. Status of the ’F225 is provided by three outputs, Input

Ready (IR), Unload Clock Output (UNCPOUT) and Output Ready

(OR). The data outputs are non–inverting with respect to the data

inputs and are disabled when the OE input is High. When OE is

Low, the data outputs are enabled to function as totem–pole outputs.

TYPE

TYPICAL SUPPLY

CURRENT

( TOTAL)

74F225

25MHz

65mA

ORDERING INFORMATION

ORDER CODE

DESCRIPTION

COMMERCIAL RANGE

PKG DWG #

20–pin plastic DIP

N74F225N

SOT146-1

20–pin plastic SOL

N74F225D

SOT163-1

INPUT AND OUTPUT LOADING AND FAN OUT TABLE

PINS

DESCRIPTION

74F (U.L.)

HIGH/LOW

LOAD VALUE

HIGH/LOW

CPA, CPB

Load clock A and load clock B inputs

1.0/0.033

20

µA/20µA

D0 – D4

Data inputs

1.0/0.033

20

µA/20µA

OE

Output enable input (active–Low)

1.0/0.033

20

µA/20µA

UNCPIN

Unload clock input

1.0/0.033

20

µA/20µA

MR

Master reset input (active–Low)

1.0/0.033

20

µA/20µA

IR

Input ready output

50/33

1.0mA/20mA

UNCPOUT

Unload clock output (active–Low)

50/33

1.0mA/20mA

Q0 – Q4

Data outputs

150/40

3.0mA/24mA

OR

Output ready output

50/33

1.0mA/20mA

NOTE: One (1.0) FAST unit load is defined as: 20

µA in the High state and 0.6mA in the Low state.

RESET MODE

A High–to–Low transition on the Master Reset (MR) input invalidates

all data stored in the FIFO by clearing the control logic and setting

OR Low. This High–to–Low transition on the MR input does not

effect the data outputs but since OR is driven Low, it signifies invalid

data on the outputs.

WRITE MODE

Data may be written into the array on the Low–to–High transition of

either load clock (CPA or CPB) input. When writing data into the

FIFO, one of the load clock inputs must be held High while the other

strobes data into the FIFO. This arrangement allows either load

clock to function as an inhibit for the other. Input Ready (IR)

monitors the status of the last word location and signifies when the

FIFO is full. This output is High whenever the FIFO is available to

accept new data. The unload clock output (UNCPOUT) also

monitors the last word location. This output generates a

Low–logic–level pulse (synchronized to the internal clock pulse)

when the last word location is vacant

READ MODE

The Output Ready (OR) output is High when valid data is present on

the data outputs. Data in the array is shifted on the Low–to–High

transition of the Unload Clock Input (UNCPIN). In order for Output

Ready (OR) to go High, Unload Clock Input (UNCPIN) must also be

High.