DTU stands for Data Terminal Unit, which functions as a lower-level GPRS transmitting terminal. During communication, DTU must be present at both ends of the link to facilitate data transmission. It handles format conversion and data sorting during the process. Below are some frequently asked questions regarding the GPRS/CDMA network and product usage:
1. What is the default configuration of the DTU? A: The default settings include 8 data bits, no parity, 1 stop bit, with a baud rate of 57600 bps and a data transfer rate of 57600 bps.
2. How can I check the current software version of the module in the DTU? A: Use the command AT+CGMR or ATI to retrieve this information.
3. When using HyperTerminal, I receive strange characters when entering AT commands. A: This may occur due to a mismatch between the serial port baud rate of HyperTerminal and that of the DTU/module. Use AT+IPR? to check the DTU’s serial port rate, then adjust HyperTerminal accordingly.
4. Is the DTU compatible with Windows 3.x, Windows 95, Windows 98, Windows NT, or Linux? A: DTU operates independently of the operating system, using a fully transparent mode. As long as the device sends data through its serial port, the DTU will function properly.
5. How do I send SMS messages in ATTEXT mode? A: First, set the mode to TEXT by entering AT+CMGF=1. Then use AT+CSDH=1 to get more detailed responses. Confirm the short message center number with AT+CSCA?. Send the message using AT+CMGS="phone number", type your message, and end with Ctrl+Z. You should see "OK" after sending.
6. Why am I unable to send SMS messages in ATPDU mode? A: Check if the PDU mode is enabled by using AT+CMGF=0. If you're unfamiliar with PDU coding, switch back to TEXT mode with AT+CMGF=1, write the message with AT+CMGW, then return to PDU mode with AT+CMGF=0 and read it with AT+CMGR.
7. How can I confirm that the DTU has connected to the GPRS/CDMA network? A: Enter AT+CGATT=1 in AT command mode. If it returns OK, then check with AT+CGATT?. A response of 1 indicates successful GPRS connection, while 0 means it's not logged in. CDMA does not support this command.
8. How do I check the signal strength and SIM/UIM card status of the DTU? A: In AT mode, enter AT+CSQ. The returned value should be in the format <**, ##>, where ** represents signal quality (higher is better), and ## should be 99. If not, check the antenna or SIM/UIM card installation, or ensure the area has GSM coverage.
9. How much redundant data is generated when sending data? A: Redundant data is only generated during the initial connection with the central unit, totaling 45 bytes. The format includes 4 hex digits (HEXID), 11-digit phone number, 0, and the login IP address.
10. How do I change the baud rate? A: In transparent mode, press “S†to enter setup mode. Use AT+IPR? to check the current baud rate, then input AT+IPR=1200. After changing the HyperTerminal’s baud rate, you can communicate at 1200 bps. For non-transparent mode, simply use AT+IPR=1200.
11. Why can’t I communicate with the DTU using my own RS232 cable? A: Your cable might be incorrectly wired. We recommend using our standard serial cable, which uses pins 2 and 3 cross-connected, and pin 5 directly connected without flow control. Keep the cable under 15 meters for optimal performance.
12. The yellow light on the DTU is off, and the device doesn't respond. A: Please refer to the user manual provided with the product for troubleshooting steps.
13. How long does it take to reboot and reconnect? A: Under normal conditions, it usually takes around 10–15 seconds to reboot and reconnect.
14. Our primary IP fails, and the DTU automatically switches to the secondary IP. Why is it switching back? A: This occurs because the primary and secondary IPs are set to Shuimu Tsinghua by default. Make sure to update both IPs if you change the primary one.
15. Why does switching between primary and secondary IPs take too long? Can we disable the secondary IP? A: Yes, you can set both primary and secondary IPs to the same address. The DTU will automatically detect whether you're using a single IP or dual IPs, saving time.
16. Why does the DTU keep restarting and showing "TcpConnectionError, NowReset"? A: This could be due to a server-side network issue. Ping your server first (e.g., ping 218.85.96.210) to verify connectivity. Ensure the firewall isn’t blocking the necessary ports.
17. Why does the DTU restart frequently with PPP errors? A: This may be caused by a faulty SIM card or GPRS network issues. Check the SIM card status and refer to question 7 for further troubleshooting.
18. Why does the DTU keep restarting and stay in "NowReStartATState"? A: If other components are functioning normally, it could be due to loose cables. Reconnect or replace the cables to resolve the issue.
19. How do I configure GPRS/CDMA DTU? A: Use HyperTerminal or a serial port test tool. Set the serial port properties to 8 data bits, no parity, 1 stop bit, and a baud rate of 57600 bps or XON/XOFF.
20. Why can't I enter AT configuration mode when setting up the DTU? A: Press and hold the "S" key on your PC before powering on the DTU. Wait until the message "GPRS-1000T Configure program: Use the extended AT commands to configure the arguments needed. Input AT+List" appears, then proceed.
21. How do I update the DTU firmware? A: Connect the DTU to your PC via COM port, run sftdnld.exe, select the COM port, and choose the *.bin file. Click "Start Download," then power on the DTU to begin the update.
22. Why does the DTU show no response or garbled text in HyperTerminal? A: This is likely due to a mismatch in baud rates. Ensure both the DTU and HyperTerminal are set to the same baud rate.
23. How is data confidentiality ensured during GPRS/CDMA transmission? A: Data is transmitted over the GPRS/CDMA network, and its security level matches that of the network itself.
24. How does the central station identify which DTU is sending data if it uses a dynamic IP? A: You can assign an ID or use the SIM card number for identification. We provide a dynamic library and demo program to help clients implement this in their central systems.
25. What if we don’t want to apply for APN or fixed IP to reduce costs? A: Use dynamic domain name resolution so the central server can access the DTU via a domain name, regardless of whether it’s static or dynamic. This reduces costs and simplifies maintenance.
26. Can the DTU be used in mobile vehicles? Is it stable at high speeds? A: The DTU is suitable for industrial environments and can be installed on moving objects. However, note that GPRS/CDMA networks may have coverage gaps in certain areas.
27. Can the DTU remain dormant for long periods to save power and traffic? A: Yes, the DTU supports remote activation. In transparent mode, it can send data upon receiving a call or SMS.
28. How can we receive data from the DTU if our server only has an internal IP? A: Configure a fixed IP on the router and set up port mapping to forward public network traffic to the internal server. Refer to your router’s manual for NAT and port mapping instructions.
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