Posted here, as although it's ultimately to be connected to an 8051, it doesn't directly involve an 8051.

I'm trying to interface to a KC21 bluetooth module (largely irrelevant), and I'm testing a few things out by connecting it to a PC serial port via a Maxim MAX3232CPE ( http://datasheets.maxim-ic.com/en/ds/MAX...AX3241.pdf ) I used 0.1 uF caps all round. Power is from a reasonably well regulated 3.2v supply.

I'm using a bog-standard circuit as per page 12 of the datasheet, no connection to the Logic side except a scope. and this is what I get when I send an 'a' to the MAX3232. First trace is the Serial port side, second is the output from the MAX3232. Naturally, when I connect the bluetooth module it doesn't see the data correctly, which is a bit disasterous as it relies on AT commands!




All worked fine at 115200, presumably because there wasn't time for the low level to climb towards VCC as much. The traces are at 19200. Some characters work fine at this speed (those without contigious strings of identical bits). I understand what's happening, but I don't understand why.

Any suggestions?