Texas Instruments SN74V245-15PAGEP

The SN74V245 is a very high-speed, low-power CMOS clocked first-in first-out (FIFO) memory. It supports clock frequencies up to 133 MHz and has read-access times as fast as 5 ns. This DSP-Sync FIFO memory features read and write controls for use in applications such as DSP-to-processor communication, DSP-to-analog front end (AFE) buffering, network, video, and data communications.

The SN74V245 is a synchronous FIFO, which means each port employs a synchronous interface. All data transfers through a port are gated to the low-to-high transition of a continuous (free-running) port clock by enable signals. The continuous clocks for each port are independent of one another and can be asynchronous or coincident. The enables for each port are arranged to provide a simple interface between DSPs, microprocessors, and/or buses controlled by a synchronous interface. An output-enable (OE) input controls the 3-state output.

The synchronous FIFO has two fixed flags, empty flag/output ready (EF/OR) and full flag/input ready (FF/IR), and two programmable flags, almost-empty (PAE) and almost-full (PAF). The offset loading of the programmable flags is controlled by a simple state machine, and is initiated by asserting the load pin (LD). A half-full flag (HF) is available when the FIFO is used in a single-device configuration.

Two timing modes of operation are possible with the SN74V245: first-word fall-through (FWFT) mode and standard mode.

In FWFT mode, the first word written to an empty FIFO is clocked directly to the data output lines after three transitions of the RCLK signal. A read enable (REN) does not have to be asserted for accessing the first word.

In standard mode, the first word written to an empty FIFO does not appear on the data output lines unless a specific read operation is performed. A read operation, which consists of activating REN and enabling a rising RCLK edge, shifts the word from internal memory to the data output lines.

The SN74V245 is depth expandable, using a daisy-chain technique or FWFT mode. The XI and XO pins are used to expand the FIFOs. In depth-expansion configuration, first load (FL) is grounded on the first device and set to high for all other devices in the daisy chain.

The SN74V245 is characterized for operation from –55°C to 125°C.