FAQs - TTL QUESTIONS

What are the differences between industrial and commercial-grade converters?
Just as there are many differences between industrial- and commercial-grade computers, the industrial- and commercial-grade converters differ in many ways, such as the level of circuit protection, temperature range and noise tolerance. Most importantly, true industrial-grade converters require rugged components and reliability-engineering designs for environmental factors, reliability, and durability, therefore, they are much more durable than commercial-grade converters. Industrial-grade converters are designed to interface with mission-critical equipment, such as computers, PLC, SCADA and HMI - whether in the field, server room, factory, control room, or fire command center.

Visit the wikipedia's pages for more information on:
Temperature classifications and Reliability engineering

 
RS232: What is DTE/DCE? How do I know my RS232 device is a DTE or a DCE?

DTE stands for Data Terminal Equipment, a PC is a DTE. DCE stands for Data Communication Equipment, a Modem is a DCE.
DTE normally comes with a Male Connector, while DCE comes with a Female Connector, but that is not always the case. Use the guide below as a simple way to confirm: Measure Pin 3 and Pin 5 (DB9 Connector) with a multi-meter. If you get a voltage of -3V to -15V, it is a DTE device. If the voltage is on Pin 2, then it is a DCE device. Note: The result for the DB-25 Connector is reversed, and Ground for the DB-25 is on Pin 7.

To learn more about RS232, check out:
RS232 basics: Three easy steps to understand and control your RS232 devices

     
RS232: What are Handshake Lines?
 

Handshake Lines are used to control the direction of data flow between DTE and DCE. They are:
RTS (Request to Send) - Asserted by DTE to prepare DCE to receive data.
CTS (Clear to Send) - RTS Acknowledgment by DCE to allow DTE to transmit.
DTR (Data Terminal Ready) - Asserted by DTE to indicate that it is ready to be connected.
DSR (Data Set Ready) - Indicates an active connection by DCE.
DCD (Data Carrier Ready) - Used by modem when a connection has been established with remote equipment.
RI (Ring Indicator) - Used by the modem to indicate a ring signal from telephone line.

 
RS232: Do I need to use handshake lines to control the data direction?

This is not necessary. The converters come with the Auto-Turnaround feature, the RS485 transceiver circuit will change the data direction automatically upon sensing a "start bit" (a logic high "Mark" to low "Space" transition) from its TTL data transmit line (TxD).

       
RS232: My control software requires handshake lines to be tied together (e.g. DTR & DCR, RTS & CTS). Can I still use your converters?

Yes, to satisfy the requirements of some software, the following handshake lines are tied together in the converters.
- Pin 1 (DCD) is connected to Pin 4 (DTR) and Pin 6 (DCR).
- Pin 7 (RTS) is connected to Pin 8 (CTS).
Note: Above pin assignments are for DTE devices.

       
RS232/TTL Distances: What are the maximum distances?
     

TTL signal has a distance limitation of ten (10) feet (about 3m), while RS232 can go up to fifty (50) feet (about 15m).

 
How do I extend the TTL distance?
     

The TTL signal has a distance limitation of 10 feet (about 3 m), while the RS485/RS422 can go up to 4000 feet (1200 m). Since TTL is a full-duplex communication, we recommend to use our full-duplex RS422/TTL converter (Model: TTL-485_422-2) to extend the 5V TTL distance to up to 4000 feet (1200 m).

If the distance is more than 4000 feet (1200 m), we would recommend to use our Serial to Fiber Optic Converter (FBR-Serial-2), together with the port-powered RS232 to TTL converters (TTL-232-1 or TTL33-232-1), to extend the TTL distances to up to 24 miles (40 km).

 
How many serial devices can I connect with the RS485/RS422 to TTL converter?
     

You can connect a maximum of 128 serial devices on RS485/RS422 side. However, this depends a great deal on a few factors such as the RS485/RS422 devices connected to the converter, data baud rate, cable distance, etc.

RS485/RS422 Termination (120-Ohm): Why is it important and when to use it?
     

RS485/RS422 network is normally used over a long distance and in an electrically noisy environment, noises, reflections, and data errors might occur if there is no termination on the RS485/RS422 buses. Both ends of the transmission lines should be terminated to reduce noises and reflections that can cause data errors. There are several methods of terminating data lines, and we recommend parallel termination. Instead of using pull-up or pull-down resistors, the parallel 120-Ohm end-of-line terminators provide a hassle-free and effective way of termination. However, since the Terminator will increase the load on the data circuit, we recommend to turn ON the Terminator only when the distance exceeds 660 feet (200m).

Note: Unlike other converters on the market that require external resistors or simply have them built-in permanently without concern for the heavy DC loading problem, our built-in 120 Ohm terminator can be easily turned ON or OFF through a simple jumper setting.

How do I perform a Loopback Test for my RS232/TTL converter?
 

Performing a Loopback Test is easy with our 232Analyzer software. Simply connect TX (TTL Out) to RX (TTL In), and then send commands from the 232Analyzer software. You should get an echo of the commands sent. By performing a simple Loopback test like this, you can test both the Transmitter and Receiver of the RS232/TTL converter. This is very helpful when you are in doubt about the performance of your converters or cables.

Click here to download a FREE copy of 232Analyzer software.

How do I perform a Loopback Test for my RS485/TTL converter?

Performing a Loopback Test is easy with our 232Analyzer software. Simply connect two RS485/TTL converters to your PC's COM ports (if your PC does not have enough COM ports, you may use USB to RS232 converters or cables). Run two instances of 232Analyzer software on your PC. When you send commands (i.e. "CommFront" in ASCII format) from one COM port, you should receive the same commands on the other, and vice versa. By performing a simple loopback test like this, you can test both the transmitter and receiver of the converter. This is very helpful when you are in doubt about the performance of your converters or cables.

Click here to download a FREE copy of 232Analyzer software.

   
How do I perform a Loopback Test for my RS422/TTL converter?

Performing a Loopback Test is easy with our 232Analyzer software. Simply connect your PC's RS422 port to the RS422 side and short TX and RX on the TTL side, and then send commands from the 232Analyzer software. You should get an echo of the commands sent. By performing a simple Loopback test like this, you can test both the Transmitter and Receiver of the RS422/TTL converter. This is very helpful when you are in doubt about the performance of your converters or cables.

Click here to download a FREE copy of 232Analyzer software.