FPGA supplies serial output data using LVTTL or LVCMOS levels to the Maxim device, which in turn, converts the logic value to the appropriate RS-232 voltage level. Likewise, the Maxim device converts the RS-232 serial input data to LVTTL levels for the FPGA. A series resistor between the Maxim output pin and the FPGA’s RXD pin protects against accidental logic conflicts.
Hardware flow control is not supported on the connector. The port’s DCD, DTR, and DSR signals connect together, as shown in Figure 7-1. Similarly, the port’s RTS and CTS signals connect together.
Figure 7-2: UCF Location Constraints for DTE RS-232 Serial Port
Figure 7-3: UCF Location Constraints for DCE RS-232 Serial Port
NET "RS232_DTE_RXD" LOC = "U8" | IOSTANDARD = LVTTL ;
NET "RS232_DTE_TXD" LOC = "M13" | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = SLOW ;
NET "RS232_DCE_RXD" LOC = "R7" | IOSTANDARD = LVTTL ;
NET "RS232_DCE_TXD" LOC = "M14" | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = SLOW ;