what is TTL cable?

[solarflow99]

Hi, I have an Icom R3 and was wondering what is so special about the serial cable it needs? I already have a DB9 serial cable that I used for a digital camera, but it doesn't seem to work. I heard there is a special cable that is TTL to rs232? Is this really true it takes a special cable?

Thanks,

 

[WA1ATA]

TTL is an old digital logic family. A "TTL to RS232" cable is a voltage level converter. Some electronic devices have a serial connection that is in RS232 format, but with voltage levels of 0 to 5V or less, while the RS-232 levels are a minimum of +/-5V, maximum of +/-15V. The "TTL to RS-232" cable boosts the TTL or 0-5V logic levels up to the higher voltages required by the RS-232 standard. These typically use the MAX232 integrated circuit from Maxim Integrated Products.

Although not guaranteed, the serial ports on most computers will will respond to TTL levels or 0-5V logic levels.

Serial ports, even those with TTL or CMOS logic levels rather than the true RS-232 voltage levels are designed to withstand being shorted out or having 12V applied. So it is relatively safe just to hook up what cables you have and see if they work.

Charlie

 

[puzzleriddle]

Ya may have better luck asking in the he Icom furum?

 

[jackj]

You may need a "null-modem" cable. This is a cable that has the Rx and Tx leads reversed. Pin 2 of a DB-9 connector is Rx data while pin 3 is Tx data. These are reversed at the other connector so that pin 2 connects to pin 3 of the other connector and pin 3 to pin 2.

 

[MarkWestin]

Your Icom, and most other receivers (and Amateur radio transceivers) uses a cable that has a "level converter" in it. Some designs use an IC chip and others use transistors. The cable converts the Computer signals which are usually 5 volts to the level that the radio uses which is usually 3.3 volts. The converter is usually located in the DB9 connector of the cable. I have a Yaesu cable which I bought for my VR-500 receiver, and it also works on my VX-7, my Icom R-5 and also worked on my Radio Shack PRO 95 when I had it. (Some of these radios require adapters for the end of the cable). The initial high cost is somewhat offset by the fact that it can be used on multiple radios. My cable also works great with a USB converter.

Mark

 

[jackj]

MarkWestin is mostly right. The original RS-232 standard called for the voltage swing to be +/- 12 vdc. Applying 12 volts to digital circuits is generally a bad idea although TTL (Transistor/Transistor Logic) circuits can handle it. A cheap and dirty level converter is a diode and a resister in series with the data lead and a 5v zener diode to ground. The diode blocks the -12 vdc, the zener diode clamps the voltage to 5 volts and the resister limits the current through the zener. You will need this circuit on each signaling lead.

 

[Butelsoftware]

You can find cheap cables for the R3 on ebay, RS232 about US$6 and the USB version about US$ 13. Search for OPC478.

Gommert
Butel Software

 

[sadatoni]

TTL - there's an acronym I haven't heard in ages.