RS232 Level Shifter

In order to interface TTL logic that is either 3.3v or 5v based to rs-232, a level shifter is required. there are a wide variety of chips available to do the job. most of the ones that are of interest to newer boards will need to be 3.3v compatible. one often referenced is the MAX233 and MAX233A. The only difference between the MAX233 and the MAX233A is the maximum data rate. the MAX233 max is 115kbaud where as the MAX233A is 230kbaud. since most console and other uart functions are all less than 115kbaud, the MAX233 is acceptable for most applications.the MAX233 version that is most common is the MAX233CPP. another version of level shifter that might be referenced is the MAX232. this is essential the same as the MAX233 but the MAX232 requires some external capacitors and the MAX233 does not. the entire series of MAX2XX chips are 5 volt powered. the MAX32XX are 3.3 volt powered. the MAX233A has been reported to be able to run at 3.3v but not at full speed.


 * Maxim-IC 5v level shifter comparison chart: http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1798
 * MAX233 versions chart: http://www.maxim-ic.com/parts.cfm/p/MAX233
 * Maxim-IC 3.3v level shifter comparison chart: http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1068
 * MAX3232 versions chart: http://www.maxim-ic.com/parts.cfm/p/MAX3232

the MAX233 and MAX232 is carried by a wide variety of distributors including:


 * http://www.jameco.com
 * http://www.digikey.com
 * http://www.bgmicro.com

if you aren't interesting in doing it from scratch there are many companies who sell a kit:


 * http://www.sparkfun.com/commerce/product_info.php?products_id=133
 * http://www.acroname.com/robotics/parts/R115-INT-BRD-KIT.html
 * http://www.bitbox.co.uk/Products/levelshift/index.htm
 * http://www.futurlec.com/Mini_RS232_TTL_3V.shtml
 * http://www.futurlec.com/Mini_RS232_TTL_5V.shtml

There are many more links to suitable modules and cables, including many USB-to-TTLSerial and cheap hackable mobile phone programming cables, here: http://www.nslu2-linux.org/wiki/HowTo/AddASerialPort