7

M67204H

4141J–AERO–04/07

Note:

1. Pointer will increment if flag is high.

Note:

1. XI is connected to XO of previous device.

See Figure 4.

Depth Expansion (Daisy

Chain) Mode

The M67204H can be easily adapted for applications which require more than 4096

words. Figure 4 demonstrates Depth Expansion using three M67204H. Any depth can

be achieved by adding additional M67204H.

The M67204H operates in the Depth Expansion configuration if the following conditions

are met:

1.

The first device must be designated by connecting the First Load (FL) control

input to ground.

2.

All other devices must have FL in the high state.

3.

The Expansion Out (XO) pin of each device must be connected to the Expansion In

(XI) pin of the next device. See Figure 4.

4.

External logic is needed to generate a composite Full Flag (FF) and Empty Flag

(EF). This requires that all EF’s and all FFs be ORed (i.e. all must be set to generate the

correct composite FF or EF). See Figure 4.

5.

The Retransmit (RT) function and Half-Full Flag (HF) are not available in the Depth

Expansion Mode.

Compound Expansion

Module

It is quite simple to apply the two expansion techniques described above together to cre-

ate large FIFO arrays (see Figure 5).

Table 1. Reset and Retransmit

Single Device Configuration/Width Expansion Mode

Mode

Inputs

Internal Status

Outputs

RS

RT

XI

Read Pointer

Write Pointer

EF

FF

HF

Reset

0

X

0

Location Zero

Location Zero

0

1

1

Retransmit

1

0

0

Location Zero

Unchanged

X

X

X

Read/Write

1

1

0

Increment

X

X

X

Table 2. Reset and First Load Truth Table

Depth Expansion/Compound Expansion Mode

Mode

Inputs

Internal Status

Outputs

RS

RT

XI

Read Pointer

Write Pointer

EF

FF

Reset First Device

0

0

(1)

Location Zero

Location Zero

0

1

Reset All Other Devices

0

1

(1)

Location Zero

Location Zero

0

1

Read/Write

1

X

(1)

X

X

X

X