I have a GT01 Panasonic LCD which it's interface is RS-232C.

I have read that the difference between RS-232 and RS-232C is their voltage level which it's ±5 V in RS232C.

Can I use a MAX232 IC to communicate with this LCD?

I'm worried that MAX232'c Voltage level (±25 V) harms the LCD.

If not, would you please propose an IC which is capable with RS-232C?


The "C" is a 1969 Specification Revision. It does not dictate 25V but is compatible with that.

Today the Spec is Ref F to expand speed, timing and low voltage enhancements and is backwards compatible.

The standard has not changed with a threshold that is the same as TTL or 1.3V = Vbe*2 but all receivers handle a wide range of Tx bipolar voltages.

Can I use a MAX232 IC to communicate with this LCD?



enter image description here

Figure 1. An oscilloscope trace of a byte transmitted by an RS232 link. Source: Wikipedia RS-232.

Note a few things:

  1. Logic is inverted. A '1' is a negative voltage and a '0' is a positive voltage.
  2. The grey area shows the valid logic level voltages. It is > 3 V for a '0' and < -3 V for a '1'.

I'm worried that MAX232'c Voltage level (±25) harms the LCD?

  1. The purpose of the MAX232 is to convert from the RS232 signal levels to the 5 V logic levels of your circuit. It is, in effect, a buffer between the two. Your LCD will never see the ±25 V.
  2. ±25 V was used to transmit over long distances at low baud rates. These days we're typically running at 9600 baud which has a limit of 15 m or so before cable capacitance becomes a problem. As a result we don't need the high voltages and if you check with a multimeter you'll find that you'll only see about ±5 to ±7 V on most devices. The reason? They're probably using the MAX232 as well.

You'll be fine if you follow the MAX232 recommended circuit and don't skip any of the decoupling capacitors, etc., recommended in their layouts.

  • \$\begingroup\$ You missed the point here. The question was if the RS232C input can handle RS232 levels. It was not about the LCD screen itself, he was asking about the LCD module if it can be damaged. \$\endgroup\$ – Dorian Dec 8 '18 at 11:42
  • \$\begingroup\$ Thanks, @Dorian. I understood the question and I thought I had addressed it with my paragraph including "Your LCD will never see the ±25 V." In almost 40 years working with all sorts of industrial RS232 interfaces I've never seen more than 12 V and that was in the days when devices had +/-12 V supplies. Most of my answer was giving background to the protocol and the buffering as there seemed to be some confusion there. \$\endgroup\$ – Transistor Dec 8 '18 at 15:36
  • \$\begingroup\$ I know that what is missing in your answer ( +-30V ipuut range for MAX232C) is in the tatasheet that OP has read but I would had a fortune if I had a penny for each call asking for something that is in the product datasheet. Make a small edit to take back my downvote. \$\endgroup\$ – Dorian Dec 9 '18 at 13:02

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