RX and TX pins interchanged with each other

[stojanmar]

While trying to verify how the code works in my protoboard version, I noticed that the RX pin that needs to be LOW to output the receive signals through the 74CBTLV3253 actually stands HIGH. TX pin has the same mistake. Looking in the code, I can see levels LOW and HIGH should be interchanged. Could this be a bug in the published code, or did I miss something else? Best Regards! Stojan

[tjlab-jf3hzb]

It works as designed. The TX (J3, No.5) pin becomes High when transmitting and Low when receiving. The RX (J3, No.4) pin has the opposite operation.

[stojanmar]

Yes, that is probably correct for J3. But for the IC U7 74CBTLV3253 , you need to invert the IC control pins 1 and 15 at the same time. Please verify the functional block diagram in the IC datasheet. You need the pin 15 to be LOW in order to operate TX mode, and pin 1 to be LOW when you operate RX. Please let me know if I read schematics wrong. BR Stojan

[tjlab-jf3hzb]

If the J3 signals are correct, the 74CBTVL3253 is being controlled correctly. In fact, no problems have occurred. Please check the circuit diagram again.

On the circuit, RX=! TX TX=! RX

[stojanmar]

I will check again and possibly run some tests with changing control levels on IC-s pins 1 and 15. Will come back here and report the results. Thanks on collaborating on my questions. BR Stojan

[stojanmar]

I confirm here that according to the circuit diagram, the levels on U7 pins 1 and 15 seems not to be correct. Lets concentrate to RX mode for now, therefore on the pin 1. During RX mode this pin has the same level as The RX (J3, No.4) pin and that is HIGH level on both. But when I look at the U7 datasheet I read that pin 1 (Enable for Output A1-pin 7) should be LOW. If HIGH the output is disconnected = floating. Please confirm-measure if you have U7-pin1 on HIGH during RX mode. If so then I suspect you are getting some weak receiver signal on A1-pin7 which is possibly there only by some parasitic capacitance of the chip or PCB layout. Again I may be wrong or read mistakenly , but here is the functional table of the U7 that I read: FUNCTION TABLE for ONE output OE S1 S0 Function L L L A Port = B1 Port L L H A Port = B2 Port L H L A Port = B3 Port L H H A Port = B4 Port H X X A Port = Disconnected

[stojanmar]

I made wrong questions! I wasn't reading circuit diagram properly. Simply I considered from your code:

define RX 47

define TX 21

But Now I see that pin1 on U7 is actually connected to TX pin 21 on ESP S3. And this one Controls the RX mode correctly. I am so sorry and apologize for making this issue wrongly. Anyhow I admire your work and will follow your project development. Particularly I like your approach about making 16Mhz IF stage that can be used on any ham bands radio and you selected esp32 which I also think is the best choice with regard to price performance. Wish you all the best! Stojan