I have a board that uses a MAX323 to connect to external serial peripherals. The board includes a device on SPI interface. When no device is connected to the MAX3232 RS-232 ports, everything is fine. When I connect a RS-232 cable to the board (to the MAX3232), interference is suddenly generated on one of the SPI related lines (not one of the 4 SPI lines, but the CE line of the connected device). This causes the SPI link to fail. By the way, no data is being sent over the serial link at the time of failure, it is simply connected to the external RS-232 peripheral. What might be the cause of this? Could it be that the waveform generated by the Tx charge pumps is causing this interference ? (but if so then it should be present all the time, why does it only manifest itself when the external device is connected).