SN74ALVC7804, SN74ALVC7806, SN74ALVC7814
512 × 18, 256 × 18, 64 × 18
LOW-POWERED FIRST-IN, FIRST-OUT MEMORIES

SCAS437C - JUNE 1994 - REVISED FEBRUARY 1996

features

• Operate at 3-V to 3.6-V V_CC
• Load Clock and Unload Clock Can Be Asynchronous or Coincident
• Low-Power Advanced CMOS Technology
• Full, Empty, and Half-Full Flags
• Programmable Almost-Full/Almost-Empty Flag
• Fast Access Times of 18 ns With a 50-pF Load and All Data Outputs Switching Simultaneously
• Data Rates From 0 to 40 MHz
• 3-State Outputs
• Pin Compatible With SN74ACT7804, SN74ACT7806, and SN74ACT7814
• Available in Shrink Small-Outline 300-mil Package (DL) Using 25-mil Center-to-Center Spacing

description

A FIFO memory is a storage device that allows data to be written into and read from its array at independent data rates. The SN74ALVC7804, SN74ALVC7806, and SN74ALVC7814 are 18-bit FIFOs with high speed and fast access times. Data is processed at rates up to 40 MHz with access times of 18 ns in a bit-parallel format. These memories are designed for 3-V to 3.6-V V_CC operation.

Data is written into memory on a low-to-high transition of the load clock (LDCK) and is read out on a low-to-high transition of the unload clock(UNCK). The memory is full when the number of words clocked in exceeds the number of words clocked out by 512. When the memory is full, LDCK has no effect on the data residing in memory. When the memory is empty, UNCK has no effect.

Status of the FIFO memory is monitored by the full (), empty (), half-full (HF), and almost- full/almost-empty (AF/AE) flags. The output is low when the memory is full and high when the memory is not full. The output is low when the memory is empty and high when it is not empty. The HF output is high whenever the FIFO contains 256 or more words and low when it contains 255 or less words. The AF/AE status flag is a programmable flag. The first one or two low-to-high transitions of LDCK after reset are used to program the almost-empty offset value (X) and the almost-full offset value (Y) if program enable (PEN\) is low. The AF/AE flag is high when the FIFO contains X or fewer words or 512 - Y or more words. The AF/AE flag is low when the FIFO contains between X + 1 and 511 - Y words.

A low level on the reset () resets the internal stack pointers and sets high, AF/AE high, HF low, and low. The Q outputs are not reset to any specific logic level. The FIFO must be reset on power up. The first word loaded into empty memory causes to go high and the data to appear on the Q outputs. The data outputs are in the high-impedance state when the output-enable () is high.

The SN74ALVC7804, SN74ALVC7806, and SN74ALVC7814 are characterized for operation from 0°C to 70°C.