diff --git a/src/bridge.c b/src/bridge.c
index 80496db..35f1fc5 100644
--- a/src/bridge.c
+++ b/src/bridge.c
@@ -114,7 +114,7 @@ int parse_ip_data(modem_config *cfg, unsigned char *data, int len)
     }
   }
   else {
-    mdm_write(cfg, (char *) data, len);
+    mdm_write(cfg, data, len);
   }
   return 0;
 }
@@ -127,7 +127,7 @@ void *ip_thread(void *arg)
   fd_set readfs;
   int max_fd;
   int res = 0;
-  char buf[256];
+  unsigned char buf[256];
   int rc;
 
 
@@ -162,8 +162,8 @@ void *ip_thread(void *arg)
         else {
           LOG(LOG_DEBUG, "Read %d bytes from socket", res);
           buf[res] = 0;
-          log_trace(TRACE_IP_IN, buf, res);
-          parse_ip_data(cfg, (unsigned char *) buf, res);
+          log_trace(TRACE_IP_IN, (char *) buf, res);
+          parse_ip_data(cfg, buf, res);
         }
       }
       if (FD_ISSET(cfg->data.cp[1][0], &readfs)) {      // pipe
@@ -248,7 +248,7 @@ void *run_bridge(void *arg)
   int max_fd = 0;
   fd_set readfs;
   int res = 0;
-  char buf[256];
+  unsigned char buf[256];
   int rc = 0;
 
   int last_conn_type;
@@ -405,7 +405,7 @@ void *run_bridge(void *arg)
           mdm_send_response(MDM_RESP_OK, cfg);
         }
         else {
-          mdm_parse_data(cfg, buf, res);
+          mdm_parse_data(cfg, (char *) buf, res);
         }
       }
 
diff --git a/src/dce.c b/src/dce.c
index 288d69b..46938c4 100644
--- a/src/dce.c
+++ b/src/dce.c
@@ -139,7 +139,7 @@ int dce_check_control_lines(modem_config *cfg)
   return new_status;
 }
 
-int dce_write(modem_config *cfg, char data[], int len)
+int dce_write(modem_config *cfg, unsigned char data[], int len)
 {
   if (cfg->dce_data.is_ip232) {
     return ip232_write(cfg, data, len);
@@ -147,7 +147,7 @@ int dce_write(modem_config *cfg, char data[], int len)
   return ser_write(cfg->dce_data.fd, data, len);
 }
 
-int dce_read(modem_config *cfg, char data[], int len)
+int dce_read(modem_config *cfg, unsigned char data[], int len)
 {
   if (cfg->dce_data.is_ip232) {
     return ip232_read(cfg, data, len);
diff --git a/src/dce.h b/src/dce.h
index d92d25f..04726fe 100644
--- a/src/dce.h
+++ b/src/dce.h
@@ -8,8 +8,8 @@ int dce_set_flow_control(modem_config *cfg, int opts);
 int dce_set_control_lines(modem_config *cfg, int state);
 int dce_get_control_lines(modem_config *cfg);
 int dce_check_control_lines(modem_config *cfg);
-int dce_read(modem_config *cfg, char *data, int len);
-int dce_write(modem_config *cfg, char *data, int len);
+int dce_read(modem_config *cfg, unsigned char *data, int len);
+int dce_write(modem_config *cfg, unsigned char *data, int len);
 
 //int dce_check_for_break(modem_config *cfg, char ch, int chars_left);
 
diff --git a/src/debug.h b/src/debug.h
index 0bf8671..05b490f 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -52,7 +52,7 @@ void log_set_file(FILE * a);
 void log_set_level(int a);
 int log_get_trace_flags();
 void log_set_trace_flags(int a);
-void log_trace(int type, unsigned char *line, int len);
+void log_trace(int type, char *line, int len);
 void log_start(int level);
 void log_end();
 
diff --git a/src/ip.c b/src/ip.c
index ae95477..4dc1bde 100644
--- a/src/ip.c
+++ b/src/ip.c
@@ -163,9 +163,9 @@ int ip_disconnect(int fd)
   return 0;
 }
 
-int ip_write(int fd, char *data, int len)
+int ip_write(int fd, unsigned char *data, int len)
 {
-  log_trace(TRACE_IP_OUT, data, len);
+  log_trace(TRACE_IP_OUT, (char *) data, len);
   return write(fd, data, len);
 }
 
diff --git a/src/ip.h b/src/ip.h
index 9fd9b48..cabe50a 100644
--- a/src/ip.h
+++ b/src/ip.h
@@ -12,6 +12,6 @@ extern int ip_connect(char addy[]);
 extern int ip_accept(int sSocket);
 extern int ip_disconnect(int fd);
 extern int ip_write(int fd, unsigned char *data, int len);
-extern int ip_read(int fd, unsigned char *data, int len);
+extern int ip_read(int fd, char *data, int len);
 
 #endif
diff --git a/src/ip232.c b/src/ip232.c
index 1c3e069..95e5112 100644
--- a/src/ip232.c
+++ b/src/ip232.c
@@ -157,7 +157,7 @@ int ip232_write(modem_config *cfg, unsigned char *data, int len)
   int text_len = 0;
 
 
-  log_trace(TRACE_MODEM_OUT, data, len);
+  log_trace(TRACE_MODEM_OUT, (char *) data, len);
   retval = len;
   if (cfg->dce_data.ip232_is_connected) {
     while (i < len) {
@@ -191,7 +191,7 @@ int ip232_read(modem_config *cfg, unsigned char *data, int len)
 {
   int res;
   int rc;
-  unsigned char buf[256];
+  char buf[256];
   int i = 0;
   int ch;
   int text_len = 0;
diff --git a/src/line.c b/src/line.c
index c829426..90cbdb5 100644
--- a/src/line.c
+++ b/src/line.c
@@ -59,7 +59,7 @@ int line_write(modem_config *cfg, char *data, int len)
     return retval;
   }
 
-  return ip_write(cfg->line_data.fd, data, len);
+  return ip_write(cfg->line_data.fd, (unsigned char *) data, len);
 }
 
 int line_listen(modem_config *cfg)
diff --git a/src/modem_core.c b/src/modem_core.c
index fe7d0fe..be53d9b 100644
--- a/src/modem_core.c
+++ b/src/modem_core.c
@@ -173,14 +173,14 @@ int mdm_set_control_lines(modem_config *cfg)
 /* Write single char bypassing parity generation since this mirrors input */
 void mdm_write_char(modem_config *cfg, char data)
 {
-  char str[2];
+  unsigned char str[2];
 
 
   str[0] = data;
   dce_write(cfg, str, 1);
 }
 
-void mdm_write(modem_config *cfg, char *data, int len)
+void mdm_write(modem_config *cfg, unsigned char *data, int len)
 {
   unsigned char *buf;
   int i;
@@ -199,7 +199,7 @@ void mdm_write(modem_config *cfg, char *data, int len)
 	buf[i] |= (((cfg->parity >> v)) & 1) << 7;
       }
     
-      dce_write(cfg, (char *) buf, len);
+      dce_write(cfg, buf, len);
       free(buf);
     }
     else
@@ -214,17 +214,17 @@ void mdm_send_response(int msg, modem_config *cfg)
 
   LOG(LOG_DEBUG, "Sending %s response to modem", mdm_responses[msg]);
   if (cfg->send_responses == TRUE) {
-    mdm_write(cfg, cfg->crlf, 2);
+    mdm_write(cfg, (unsigned char *) cfg->crlf, 2);
     if (cfg->text_responses == TRUE) {
       LOG(LOG_ALL, "Sending text response");
-      mdm_write(cfg, mdm_responses[msg], strlen(mdm_responses[msg]));
+      mdm_write(cfg, (unsigned char *) mdm_responses[msg], strlen(mdm_responses[msg]));
     }
     else {
       LOG(LOG_ALL, "Sending numeric response");
       sprintf(msgID, "%d", msg);
-      mdm_write(cfg, msgID, strlen(msgID));
+      mdm_write(cfg, (unsigned char *) msgID, strlen(msgID));
     }
-    mdm_write(cfg, cfg->crlf, 2);
+    mdm_write(cfg, (unsigned char *) cfg->crlf, 2);
   }
 }
 
@@ -389,8 +389,8 @@ int mdm_parse_cmd(modem_config *cfg)
         strncpy(cfg->dialno, cfg->last_dialno, strlen(cfg->last_dialno));
         cfg->dial_type = cfg->dial_type;
         cfg->memory_dial = TRUE;
-        mdm_write(cfg, cfg->crlf, 2);
-        mdm_write(cfg, cfg->dialno, strlen(cfg->dialno));
+        mdm_write(cfg, (unsigned char *) cfg->crlf, 2);
+        mdm_write(cfg, (unsigned char *) cfg->dialno, strlen(cfg->dialno));
       }
       else {
         cfg->dialno[0] = 0;
@@ -477,7 +477,7 @@ int mdm_parse_cmd(modem_config *cfg)
       break;
     case AT_CMD_FLAG_QUERY | 'S':
       sprintf(tmp, "%s%3.3d", cfg->crlf, cfg->s[num]);
-      mdm_write(cfg, tmp, strlen(tmp));
+    mdm_write(cfg, (unsigned char *) tmp, strlen(tmp));
       break;
     case 'T':  // defaut to tone dialing
       //cfg->default_dial_type=MDM_DT_TONE;
@@ -603,7 +603,7 @@ int mdm_handle_char(modem_config *cfg, char ch)
   if (cfg->cmd_started == TRUE) {
     if (ch == (char) (cfg->s[SRegisterBackspace])) {
       if (cfg->cur_line_idx == 0 && cfg->echo == TRUE) {
-        mdm_write(cfg, "T", 1);
+        mdm_write(cfg, (unsigned char *) "T", 1);
       }
       else {
         cfg->cur_line_idx--;
diff --git a/src/modem_core.h b/src/modem_core.h
index 8c7360a..6063424 100644
--- a/src/modem_core.h
+++ b/src/modem_core.h
@@ -145,7 +145,7 @@ typedef struct modem_config {
   int disconnect_delay;
   char crlf[3];
   int parity;
-  unsigned char pchars[3];
+  char pchars[3];
 } modem_config;
 
 int mdm_init(void);
diff --git a/src/nvt.c b/src/nvt.c
index 2e7bb45..a9fbec6 100644
--- a/src/nvt.c
+++ b/src/nvt.c
@@ -120,7 +120,7 @@ int parse_nvt_subcommand(int fd, nvt_vars *vars, unsigned char *data, int len, i
   return rc;
 }
 
-void send_nvt_command(int fd, nvt_vars *vars, unsigned char action, int opt)
+void send_nvt_command(int fd, nvt_vars *vars, int action, int opt)
 {
   unsigned char cmd[3];
 
diff --git a/src/nvt.h b/src/nvt.h
index 2686eb2..a75526b 100644
--- a/src/nvt.h
+++ b/src/nvt.h
@@ -45,13 +45,13 @@ typedef enum {
 typedef struct nvt_vars {
   int binary_xmit;
   int binary_recv;
-  unsigned char term[256];
+  char term[256];
 } nvt_vars;
 
 extern void nvt_init_config(nvt_vars *vars);
 extern int get_nvt_cmd_response(int action, int type);
 extern int parse_nvt_subcommand(int fd, nvt_vars *vars, unsigned char *data, int len, int speed);
-extern void send_nvt_command(int fd, nvt_vars *vars, unsigned char action, int opt);
+extern void send_nvt_command(int fd, nvt_vars *vars, int action, int opt);
 extern void parse_nvt_command(int fd, nvt_vars *vars, nvtCommand action, nvtOption opt, int parity);
 
 #endif
diff --git a/src/serial.c b/src/serial.c
index cc1e6d0..5025d32 100644
--- a/src/serial.c
+++ b/src/serial.c
@@ -173,18 +173,18 @@ int ser_set_control_lines(int fd, int state)
   return 0;
 }
 
-int ser_write(int fd, char *data, int len)
+int ser_write(int fd, unsigned char *data, int len)
 {
-  log_trace(TRACE_MODEM_OUT, data, len);
+  log_trace(TRACE_MODEM_OUT, (char *) data, len);
   return write(fd, data, len);
 }
 
-int ser_read(int fd, char *data, int len)
+int ser_read(int fd, unsigned char *data, int len)
 {
   int res;
 
 
   res = read(fd, data, len);
-  log_trace(TRACE_MODEM_IN, data, res);
+  log_trace(TRACE_MODEM_IN, (char *) data, res);
   return res;
 }
diff --git a/src/serial.h b/src/serial.h
index 7175984..5fe588a 100644
--- a/src/serial.h
+++ b/src/serial.h
@@ -11,7 +11,7 @@ int ser_init_conn(char *tty, int speed);
 int ser_set_flow_control(int fd, int status);
 int ser_get_control_lines(int fd);
 int ser_set_control_lines(int fd, int state);
-int ser_write(int fd, char *data, int len);
-int ser_read(int fd, char *data, int len);
+int ser_write(int fd, unsigned char *data, int len);
+int ser_read(int fd, unsigned char *data, int len);
 
 #endif
diff --git a/src/tcpser.c b/src/tcpser.c
index 5886e8d..b6ca36e 100644
--- a/src/tcpser.c
+++ b/src/tcpser.c
@@ -130,7 +130,7 @@ int main(int argc, char *argv[])
           cSocket = ip_accept(sSocket);
           if (cSocket > -1) {
             if (strlen(all_busy) < 1) {
-              ip_write(cSocket, (char *) MDM_BUSY, strlen(MDM_BUSY));
+              ip_write(cSocket, (unsigned char *) MDM_BUSY, strlen(MDM_BUSY));
             }
             else {
               writeFile(all_busy, cSocket);