Screaming Circuits: Rs232 Redux


Rs232 Redux

A few years ago, the death of RS232 was all over the trade press. USB did, of course, do a lot of damage to the communications standard where PC's are concerned, but other than that, RS232 is far from dead. It is, in fact, very common in the microcontroller and small embedded world.

Chip to Chip tends to use I2C, SPI, JTAG or CAN protocols but the lowly RS232 is almost always around to allow universal communications with PC's, terminals, programmers or other miscellaneous devices.

In the old days, RS232 was quite the pain when working in the digital world. Everything else could get by with a simple regulated 5 Volt supply, while the comm port required + and - 12V. If you had a few op-amps or comparators, you might already have the +/- 12 supplies, but otherwise, it was just a bunch of added junk and wasted space.

In come the MAX232 and other similar chips. With four ceramic capacitors, this little chip could create standards compliant RS232 from a single + 5 Volt supply. I'm not exactly sure which manufacturer or variant was first, but the Max232 seems to be the most well known. Many are pin-compatible with the Max232, which has two transmit and two receive lines. I've seen others with as many as ten transmit or receive lines.

St3243_flipchip_footprint I've used a lot of these in a 16-pin SOIC narrow package but recently, I was looking for a size reduction. I found a part from ST Micro in a 5 x 6 ball flip-chip BGA package - the ST3243EBJR. It measures just 4mm X 2.5mm. It has three transmitters and five receivers. I'll put the five 0402 caps (four for the charge pump and one bypass) on the back side of the board for an amazingly efficient use of board space.

Duane Benson
Let's get small

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