• We recently switched our forum platform. If you experience any issues please email support@crystalfontz.com

HELP - CFA735-TFK-KR "TTL SERIAL INVERTED"

veneridesign

New member
Hello,
I'm trying to interface a CFA735-TFK-KR to a GPIO (0-3,3V).
My problem is : the display serial inverted protocol is

Bit start=1 --DATA--Bit stop=0

OR

Bit start=0 --DATA--Bit stop=1

Thank you for help, I try to find this simple information ,but i found a lot of contradictory meanings...

Luca
Looking for additional LCD resources? Check out our LCD blog for the latest developments in LCD technology.
 

CF Tech

Administrator
Ref: "Serial Communication Using RS-232 by Christian Blum"
http://www.z80.info/1656.htm


RS-232 signals on a "real" serial port look like this. These are the signals you would get if you had a CFA-735 with a CFA-RS232-01 installed:

Code:
The TTY protocol uses two different line states called 'mark' and 'space'.
(For the sake of clearness I name the line states 'high' (voltage) for
positive and 'low' (voltage) for negative voltages). If no data is
transmitted, the line is in its quiescent 'low' ('mark') state or in the
'break' state ('high'). Data looks like

      space            +---+       +---+   +---+         high  '0' +5v ~ +12v
                       |   |       |   |   |   |
      mark   ----------+   +-------+   +---+   +-------  low   '1' -5v ~ -12v

                        (1)  --------(2)-------- (3)

  (1) start bit   (2) data bits   (3) stop bit(s)
If you have the CFA-RS232-01 installed, use "N,8,1" (No parity, 8 data bits, 1 stop bit). The connection is then made to a "real" serial port, like you would find on a PC.

The CFA-RS232-01 has a RS232 level translator chip on it, and these chips have traditionally inverted the signal sense (ref: http://www.exar.com/connectivity/transceiver/rs232/sp3220e ) so the signals before this ship are inverted compared to after it.

If you do not have the CFA-RS232-01 installed, then you are accessing the UART's Rx and Tx lines directly and the data looks like:

Code:
      mark   ----------+   +-------+   +---+   +-------  high  '1' ~ 3.3v
                       |   |       |   |   |   |
      space            +---+       +---+   +---+         low  '0' ~0v

                        (1)  --------(2)-------- (3)

  (1) start bit   (2) data bits   (3) stop bit(s)
It is still "N,8,1" but you need to feed the signals to your microcontroller's UART Rx and Tx pins, like you would find on an Arduino or similar.
 
Top