Xilinx introduces the XC18V00 series of in-system programmable configuration PROMs (Figure 1). Devices in this 3.3V family include a 4-megabit, a 2-megabit, a 1-megabit, and a 512-kilobit PROM that provide an easy-touse, cost-effective method for reprogramming and storing Xilinx FPGA configuration bitstreams.

When the FPGA is in Master Serial mode, it generates a configuration clock that drives the PROM. A short access time after CE and OE are enabled, data is available on the PROM DATA (D0) pin that is connected to the FPGA DIN pin. New data is available a short access time after each rising clock edge. The FPGA generates the appropriate number of clock pulses to complete the configuration. When the FPGA is in Slave Serial mode, the PROM and the FPGA are clocked by an external clock.

When the FPGA is in Master SelectMAP mode, the FPGA generates a configuration clock that drives the PROM. When the FPGA is in Slave Parallel or Slave SelectMAP mode, an external oscillator generates the configuration clock that drives the PROM and the FPGA. After CE and OE are enabled, data is available on the PROM’s DATA (D0-D7) pins. New data is available a short access time after each rising clock edge. The data is clocked into the FPGA on the following rising edge of the CCLK. A free-running oscillator can be used in the Slave Parallel or Slave SelecMAP modes.

Multiple devices can be cascaded by using the CEO output to drive the CE input of the following device. The clock inputs and the DATA outputs of all PROMs in this chain are interconnected. All devices are compatible and can be cascaded with other members of the family or with the XC17V00 one-time programmable serial PROM family.