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TTL/RS-232 Conversion circuit interface

Hi All,

I am interfacing a ham radio to a computer to program it and I have been looking at various TTL / RS-232 conversion circuits. However I happen to have a commercial ADMS programming cable I use with my Yaesu VX-7R radio (ham radio). This cable also handles this type of conversion so I am thinking why reinvent the wheel when I can utilize this existing circuit which is already integrated into the D-sub shell of this cable.

Thus my question:

These generic circuits appear to RS-232 logic levels (+/-12VDC) on pins 2 &

3 of a DB9 connector and converts them to 0 & 5VDC. Which TTL voltage corresponds to a logic 0 and which to a logic 1? On the RS-232 side, the data pins use negative logic, so +3 to +12 VDC is logic 0 and -3 to -12VDC is logic 1. Does the TTL data input use positive logic instead ( logic 1 is +5VDC and logic 0 is 0VDC)?

What is the industry convention when terminating the TTL side of this cable to a stereo plug. ... is the tip conductor logic 1 or logic 0? Once I determine this, then I will use this existing conversion cable and simply wire the stereo plug conductors to their respective TXD and RXD pins on my Yaesu FT-857.

Lastly, what happens if one connects the TTL level TX conductor to the TXD pin on the radio side accidentally instead of the RXD pin on the radio? i.e. wires crossed in error

Thanks for any and all info!

73's Will
Reply to
Will
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on the RS232 side data marking condition is defined as a negative voltage i.e. mark -3v to -12 = +5V on the TTL side

Reply to
Ryan weihl

Hi Ryan,

One more related question:

On the RS-232 side, the TXD side is typically held in a mark state (logic 1) if I recall correctly (hence -3v to -12v) until the next byte for transmision. If I view the TTL side of this TXD line, should I expect to see this pin pulled up to 5V?

Essentially, what I would like to do is be able to differentiate between the TXD and RXD TTL level pins on a dual channel scope to double check my interface to the radio. Thus, with this conversion cable connected to a computer with an active Hyperterminal and holding a given keyboard key down.

--Will

2 &

the

to -12VDC

1 is
Reply to
Will

yes, on the TTL side mark = +5v, and thats the way the RS232 chips work. Max or Dallas or whatever

TXd and RXd will both be logic 1 in idle mode i.e. +5V on the ttl and -3 to -12V on the RS232 side

Reply to
ryan wiehle

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