ESP8266 Community Forum

- Mon Oct 09, 2017 1:55 am #70735

The modification for 7 bits is extremely simple, have you looked at SoftwareSerial.cpp?
Note: rxRead() might trick you, since it is written using 0x80 and right shift. I'd change it to 0x01 and left shift, so it can handle 7-bit correctly simply by changing the loop limit.

I'd mod software serial to have a method for setting a variable for bits., rather than constant 8.

These mods would take a minute to do. It might take a few minutes, or an hour, to figure out. Hint: there are two loops with 8 hard-coded, and one place where 0x80 is OR'ed into the received byte.

Dear tele_player,
thanks for your reply and the guiding. For my needs I will not use receiving data at all, so, in my case it is better to remove all rx parts in the software serial routine.
With the above in mind, can you modify the software serial ( .cpp & .h ) to meet my need?
I asking this because I am not sure that I can do it by myself even if it simple as you told.
In all cases thanks for your helping hand.
Best Regards,
Mike Kranidis

- Mon Oct 09, 2017 12:10 pm #70745 Do you have a device which can receive this protocol?

- Mon Oct 09, 2017 3:58 pm #70751

Do you have a device which can receive this protocol?

yes, actually this type of bit stream is a Navtex coded. So I have a receiver using this I can confirm the correct bit stream. Also I can use Logic Analyzer.
What next?

- Mon Oct 09, 2017 10:44 pm #70755 I don't want to get into figuring out what version you have installed, and I don't know what may or may not have changed, but here's the relevant function grabbed from somewhere on Github.
I've added comments showing what I changed to transmit 7 bits, no start, no stop. My comments will start with ***

Caveat: I haven't compiled this, or tested it, and I have little confidence that this will be of any use to you.

Code: Select all
size_t SoftwareSerial::write(uint8_t b) {
   if (!m_txValid) return 0;

   if (m_invert) b = ~b;
   // Disable interrupts in order to get a clean transmit
   cli();
   if (m_txEnableValid) digitalWrite(m_txEnablePin, HIGH);
   unsigned long wait = m_bitTime;
   digitalWrite(m_txPin, HIGH);
   unsigned long start = ESP.getCycleCount();
    // Start bit;
//   digitalWrite(m_txPin, LOW);   // *** disable START bit
//   WAIT;          // *** disable START bit
   for (int i = 0; i < 7; i++) {.  // *** Was 8
     digitalWrite(m_txPin, (b & 1) ? HIGH : LOW);
     WAIT;
     b >>= 1;
   }
   // Stop bit
//   digitalWrite(m_txPin, HIGH);  // *** disable STOP bit
//   WAIT;   // *** disable STOP bit
   if (m_txEnableValid) digitalWrite(m_txEnablePin, LOW);
   sei();
   return 1;
}