http://www.hpl.hp.com/personal/Jean_Tourrilhes/bt/setserial_16C950-2.diff

diff -u -p setserial.brain.c setserial.c
--- setserial.brain.c	Mon Oct 29 16:49:10 2001
+++ setserial.c	Mon Oct 29 17:01:54 2001
@@ -77,6 +77,7 @@ struct serial_type_struct {
 #define CMD_FLOW_ON     16
 #define CMD_RX_TMOUT    17
 #define CMD_DMA_CHAN    18
+#define CMD_WMSR        19
 
 #define FLAG_CAN_INVERT	0x0001
 #define FLAG_NEED_ARG	0x0002
@@ -126,9 +127,15 @@ struct flag_type_table {
 	CMD_RX_TMOUT,   "rx_timeout",   0,              0,              0, FLAG_NEED_ARG,
 	CMD_DMA_CHAN,   "dma_channel",  0,              0,              0, FLAG_NEED_ARG,
 #endif
+	CMD_WMSR,	"wmsr",		0,		0,		0, FLAG_NEED_ARG,
 	0,		0,		0,		0,		0, 0,
 };
 	
+/* Kernel header will take ages before beeing updated in distributions */
+#ifndef TIOCSERSETWMSR
+#define TIOCSERSETWMSR  0x5461	/* Set custom write in Modem Status Register */
+#endif	/* TIOCSERSETWMSR */
+
 char *serial_type(int id)
 {
 	int i;
@@ -603,6 +610,15 @@ void set_serial(char *device, char ** ar
 			set_hayesesp(fd, p->cmd, atonum(*arg++));
 			break;
 #endif
+		case CMD_WMSR:
+			{
+				unsigned char wmsr = atonum(*arg++);
+				if (ioctl(fd, TIOCSERSETWMSR, &wmsr) < 0) {
+					perror("Cannot set wmsr");
+					exit(1);
+				}
+			}
+			break;
 		default:
 			fprintf(stderr, "Internal error: unhandled cmd #%d\n", p->cmd);
 			exit(1);