Configuration Handbook - Kamami.pl

Configuring APEX 20KE & APEX 20KC DevicesIf your system requires to bus-share the DATA[7..0] line, you can workaroundthis by ensuring that the second (or next) device sees correctconfiguration data on the first rising edge of DCLK after the nCEO signalgoes low. This can be achieved by delaying the nCEO signal by usingexternal registers or by presenting the next byte of configuration dataafter the nCEO transition.All other configuration pins (nCONFIG, nSTATUS, DCLK, DATA[7..0],and CONF_DONE) are connected to every device in the chain. You shouldpay special attention to the configuration signals because they mayrequire buffering to ensure signal integrity and prevent clock skewproblems. Specifically, ensure that the DCLK and DATA lines are bufferedfor every fourth device. Because all device CONF_DONE pins are tiedtogether, all devices initialize and enter user mode at the same time.Since all nSTATUS and CONF_DONE pins are tied together, if any devicedetects an error, configuration stops for the entire chain and the entirechain must be reconfigured. For example, if the first FPGA flags an erroron nSTATUS, it resets the chain by pulling its nSTATUS pin low. Thisbehavior is similar to a single FPGA detecting an error.If the Auto-Restart Configuration on Frame Error option is turned on, theFPGAs release their nSTATUS pins after a reset time-out period(maximum of 40 µs). After all nSTATUS pins are released and pulled high,the microprocessor can try to reconfigure the chain without needing topulse nCONFIG low. If this option is turned off, the microprocessor mustgenerate a low-to-high transition (with a low pulse of at least 8 µs) onnCONFIG to restart the configuration process.In your system, you may have multiple devices that contain the sameconfiguration data. To support this configuration scheme, all device nCEinputs are tied to GND, while nCEO pins are left floating. All otherconfiguration pins (nCONFIG, nSTATUS, DCLK, DATA[7..0], andCONF_DONE) are connected to every device in the chain. You should payspecial attention to the configuration signals because they may requirebuffering to ensure signal integrity and prevent clock skew problems.Specifically, ensure that the DCLK and DATA lines are buffered for everyfourth device. Devices must be the same density and package. All deviceswill start and complete configuration at the same time. Figure 7–18 showsmulti-device PPS configuration when both devices are receiving the sameconfiguration data.Altera Corporation 7–39August 2005 Configuration Handbook, Volume 1