Level translation details

2 thoughts on “Level translation details

  1. According to hardware user guide:

    In order to interface the GL865 with a PC com port or a RS232 (EIA/TIA-232) application a
    level translator is required. This level translator must:
    • invert the electrical signal in both directions;
    • change the level from 0/2.8V to +15/-15V.

    I’m a bit confused about the first part. Is level inversion actually required and why? I’m asking because there is a module based on GL865 out there (MikroElektronika GSM Click), which uses TXB0106 as a voltage translator, which is noninverting, and it work fine.

    1. The EVK2 uses MAX3237 which is an inverting chip. CMOS (also TTL) and RS232 levels are inverted, RS232 MARK is negative and SPACE is positive hence 0v CMOS -> +15V RS232 and 2.8V CMOS -> -15V RS232.

      I had a quick look at Mikroelektronika’s GSM Click: is a little nice board meant to be interfaced with a microcontroller (not PC) which has the same CMOS/TTL signal conventions, the TXB0106 chip acting as a noninverting voltage level translator to fit the host.