ESP8266 Community Forum

- Thu Aug 13, 2015 3:35 pm #25928 Hi Mike,

According to 0A-ESP8266__Datasheet__EN_v4.3.pdf document the, the input voltage should with the following ranges :
Vil Min=-0.3V Max=0.25xVIO
Vih Min=0.75xVIO Max=3.3 V

Excuse me for my brain slowness, but why do you need an inverter on Rx ?

- Fri Aug 14, 2015 3:31 am #25944 Hi Martin

Thanks for the data. Is there any info on the internal pullup current? This will determine the minimum drive impedance to give the required logic low on the Rx pin.

I need an inverter only because I have added logic between the PIC , the PC and the ESP. In order to diagnose why my ESP is not working via the PIC, but works from a PC with what is meant to be the same data strings, I have created a logic circuit between the PIC Tx/Rx, the PC Tx / Rx and the ESP Tx/Rx. I can now try it with various combinations and monitor what is going on. With just the PC to ESP, the HIN232 IC does the inversion from RS232 to the ESP levels. This is the arrangement I have used for 'flashing' the ESP previously.

Also another question. (Maybe the wrong Forum?) . If I do a hard reset on the ESP, I get a long string of non-ASCII chars ( a bit of a nuisance for a standalone application) but in this string is the sequence 'MEM. CHECK FAIL'. The ESP still works but should I be concerned?

With a power-on reset, the ESP gives an even longer (270 chars) string of 'garbage'. As the PIC powers up at the same time, this garbage is fed directly to the PIC which overflows its 256 byte buffer and makes a bit of a mess. Is there a way of suppressing this reset string?

Regards

Mike B

- Fri Aug 14, 2015 9:26 am #25964 My brain slowness mode still active : you're using HIN232 because you have a real RS232 port on your PC ? Why it needs to be inverted again, (the inversion is only at the +/- 12V of the RS232 signal level) ? So, I don't see the needs for an inverter. Maybe a schematic here will make me understand ...

About the internal pullups, Expressif documents don't mentioned their values, but I presume they are "weak", probably something like 47K or 100K. But don't rely on them.

About the boot message, it is sent at 74800 baud, and there is no way to get rid of it, it is probably sent by ROM bootloader itself. Beware also that some Serial-USB don't handle such baud rate.

- Fri Aug 14, 2015 1:22 pm #25981 Hi Martin

Yes, I have a real RS232 port. I have had bad experiences with serial to USB converters, especially at 115200B. Hence the HIN232 IC. This inverts the RS232 and gives 5V logic levels. I reduce the output to 3.3V for the ESP. The input to the HIN232 works with 3.3V OK. As I tried to explain, I have constructed an adapter board containing 4000 series logic. As this uses NAND gates, it inverts again so I need to invert it back. The adapter is so I can look at both the PIC and ESP outputs on my PC and send to the ESP from either as well. It is purely for diagnostics as I couldn't get the ESP to work properly from the PIC but could from the PC and wanted to find out why.

I was asking about the pullups as my 4000 series logic at 3.3V supply would not give a logic low on the ESP input. I have fixed this by using a transistor instead of logic to do the final inversion. It works now anyway.

If the boot message is at 74800 B, then I am surprised that both the PIC and my PC receive it OK even though they are set to 115200B. If it can't be removed, I can arrange to ignore it.

Regards

Mike B