My MB has builtin UARTs (Supermicro X10SAE).  I've got an external modem hooked up to /dev/ttyS0.  I'm running CentOS7.Without minicom running on /dev/ttyS0:The modem has CTS on.With minicom running on /dev/ttyS0:The modem lights up RTS and DTR along with CTS.Typing text into minicom does NOT light up the TX/RX lightsAT does nothing+++ does nothingATDT does nothingIf I move the modem (on the same box!) to a usb/serial convertor, and connect minicom to /dev/ttyUSB0, the modem responds.[root ~]#  setserial -a /dev/ttyS0/dev/ttyS0, Line 0, UART: 16550A, Port: 0x03f8, IRQ: 4        Baud_base: 115200, close_delay: 50, divisor: 0        closing_wait: 3000        Flags: spd_normal skip_test[root ~]# setserial -a /dev/ttyUSB0 /dev/ttyUSB0, Line 0, UART: 16654, Port: 0x0000, IRQ: 0        Baud_base: 460800, close_delay: 0, divisor: 0        closing_wait: infinte        Flags: spd_normalI called the modem while on /dev/ttyS0 and saw a blip on TX for the RING, but it did not show on the screen.I assume I have the right port -- I even moved it to ttyS1 for comparison.  No difference.I'm stumped!  Ideas?  I'm beginning to wonder if the MB header to serial jack ribbon cable -- both!? -- are defective somehow.
Serial port's modem lights up, but can't communicate
serial port;modem;minicom
Ah, thanks to a colleague at lunch who pointed out there isn't a single standard for serial headers.From the X10SAE manual:And I see a cable store that sells crossed and straight:* CROSSED PINOUT * 18 Serial Port Cable DB-9 Male TO 10 PIN IDC Socket* STRAIGHT PINOUT * 18 Serial Port Cable DB-9 Male TO 10 PIN IDC Socket I'll try hand rewiring the cables tonight, and if it works, I'll accept this answer.