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RL-ARM User's Guide (MDK v4)

RL-RTX RL-FlashFS RL-TCPnet TCP Socket Opening TCP Connection TCP Active Open TCP Passive Open Sending TCP Data Example for Sending Data Multiple TCP Connections UDP Socket Opening UDP Connection Sending UDP Data When DHCP Enabled When ARP Cache Empty Example for Sending Data IP Multicasting Multiple UDP Connections Configuring RL-TCPnet Static Configuration System Definitions Ethernet Network Interface PPP Network Interface SLIP Network Interface UDP Socket TCP Socket BSD Socket HTTP Server Telnet Server TFTP Server TFTP Client FTP Server FTP Client DNS Client SMTP Client SNMP Agent SNTP Client Error Function Runtime Configuration Library Files Using RL-TCPnet Stand Alone With RTX Kernel Event Driven Operation IP Address Assignment Ethernet Interface PPP Interface SLIP Interface Localhost Applications HTTP Server Script Language CGI Functions Ajax Support Using XML XML Example How it works SOAP Support SOAP Interface Large POST Messages Web Pages Default Page Error Pages Web on SD Card Web Update File System Interface Http Caching How it works Internal Web External Web Multi-user Authentication Using RAM File System FCARM File Converter PRINT Directive NOPRINT Directive PAGEWIDTH Directive PAGELENGTH Directive ROOT Directive Telnet Server Command Line Interface Multi-user Authentication Sending Reply Message Short Reply Long Reply Continuous Screen Update TFTP Server File System Interface TFTP Client File System Interface FTP Server File System Interface Multi-user Authentication Supported Commands FTP Client File System Interface SMTP Client SNMP Agent MIB Database MIB Interface MIB Entry MIB Table DNS Resolver Starting DNS Device Drivers Ethernet Driver Interrupt Mode Modem Driver Serial Driver Using Serial Link Cable Connection Modem Connection Windows Dial-up Add Direct Serial Link New Dial-up Connection Configure PPP Dial-up Configure SLIP Dial-up Debugging Enabling Debug Debug Level Redirecting Output Function Overview BSD Routines CGI Routines Ethernet Routines FTP Routines HTTP Routines IGMP Routines Miscellaneous Routines Modem Routines PPP Routines Serial Routines SLIP Routines SMTP Routines SNMP Routines System Functions TCP Routines Telnet Routines TFTP Routines UDP Routines RL-CAN RL-USB Example Programs Library Reference Appendix

Modem Driver

The Modem Driver controls an attached modem, dials an outgoing target number, and handles incoming calls. The Modem Driver is used when the PPP or SLIP serial network interface is enabled. You must use a Null_Modem driver for the zero-modem link if you use a serial cable to connect the embedded device directly to a computer.

The required functions for the driver are:

RL-TCPnet includes two modem device drivers which are located in the \Keil\ARM\RL\TCPnet\User directory:

  • Null_Modem.c is a zero-modem link driver used when a computer is connected directly to the target hardware. The computer simulates a real modem. The Null_Modem driver responds to modem commands sent from a computer in the same way as it responds to a real modem. It also works with the direct cable connection link supported by MS Windows.
  • Std_Modem.c is a standard modem driver. This driver works with most of the currently available modems. Use the standard modem driver when a real modem is used to access the embedded device over a public telephone network.

You can copy these files into your project folder or use them as a template to write your own modem driver.


  • You need to include only one modem driver into your project for the PPP or SLIP interface. For a zero-modem link, this is not required because the default Null_Modem driver is already in the RL-TCPnet library.
  • If you want to customize the Null_Modem.c modem driver, copy it from the \Keil\ARM\RL\TCPnet\User directory and add it to your project. Then customize it as needed.
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