SER_DSR
| (!(status & SER_DSR) ? TIOCM_DSR : 0)
if(!(status & SER_DSR))
ciab.ddra &= ~(SER_DCD | SER_CTS | SER_DSR); /* inputs */
unsigned char status = ciab.pra & (SER_DCD | SER_CTS | SER_DSR);
if (dstatus & SER_DSR)
current_ctl_bits = ciab.pra & (SER_DCD | SER_CTS | SER_DSR);