CY7C4235V

The CY7C42X5V are high-speed, low-power, first-in first-out (FIFO) memories with clocked read and write interfaces. All are 18 bits wide. The CY7C42X5V can be cascaded to increase FIFO depth. Programmable features include Almost Full/Almost Empty flags. These FIFOs provide solutions for a wide variety of data buffering needs, including high-speed data acquisition, multiprocessor interfaces, and communications buffering.

These FIFOs have 18-bit input and output ports that are controlled by separate clock and enable signals. The input port is controlled by a Free-Running Clock (WCLK) and a Write Enable pin (WEN).

When WEN is asserted, data is written into the FIFO on the rising edge of the WCLK signal. While WEN is held active, data is continually written into the FIFO on each cycle. The output port is controlled in a similar manner by a Free-Running Read Clock (RCLK) and a Read Enable pin (REN). In addition, the CY7C42X5V have an Output Enable pin (OE). The read and write clocks may be tied together for single-clock operation or the two clocks may be run independently for asynchronous read/write applications. Clock frequencies up to 66 MHz are achievable.

Retransmit and Synchronous Almost Full/Almost Empty flag features are available on these devices.

Depth expansion is possible using the Cascade Input (WXI, RXI), Cascade Output (WXO, RXO), and First Load (FL) pins.

The WXO and RXO pins are connected to the WXI andRXI pins of the next device, and the WXO and RXO pins of the last device should be connected to the WXI and RXI pins of the first device. The FL pin of the first device is tied to V_SS and the FL pin of all the remaining devices should be tied to V_CC.

The CY7C42X5V provides five status pins. These pins are decoded to determine one of five states: Empty, Almost Empty, Half Full, Almost Full, and Full (see Table 2). The Half Full flag shares the WXO pin. This flag is valid in the stand-alone and width-expansion configurations. In the depth expansion, this pin provides the expansion out (WXO) information that is used to signal the next FIFO when it will be activated.

The Empty and Full flags are synchronous, i.e., they change state relative to either the Read Clock (RCLK) or the write clock (WCLK). When entering or exiting the Empty states, the flag is updated exclusively by the RCLK. The flag denoting Full states is updated exclusively by WCLK. The synchronous flag architecture guarantees that the flags will remain valid from one clock cycle to the next. As mentioned previously, the Almost Empty/Almost Full flags become synchronous if the V_CC/SMODE is tied to VSS. All configurations are fabricated using an advanced 0.65 P-Well CMOS technology. Input ESD protection is greater than 2001V, and latch-up is prevented by the use of guard rings.