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October 14, 2007
about 3 years ago
It would be interesting if there was a way to rearrange the pinout so that VCCIO, VCC, and GND are next to each other in that order. This would make it easier to add a three pin TO92 LDO regulator for 1.8v (or anything else), which is the only feature this board is missing. It would also be possible to put a thru hole (or solder jumper) for V3.3 next to VCCIO (inside the current row of pins). This pin arrangement could be solder jumpered directly, removing the need for separate solder jumper. Maybe all this was tried and it didn’t fit…
Also, the features of the FT232H are worth looking into to make a similar board (even if you use a similar form factor and can’t breakout all the pins). There are a number additional features, but the main one is that the buffer of the FT232R is so small that if you bitbang (8 bits wide) out more then (I think) 64 cycles, it breaks it up into multiple usb packets, which causes large pauses in the signals until the next packet arrives which is no good for some applications. FT232H also allows a HUGE pattern length if you’re only toggling or reading one pin.
The main difference is the FT232H has a sequencer that allows you to make cycle accurate timing (even “pause for input change” on one pin!) on the 8 bit bus which enables a much larger application space, whereas the FT232R does not have this sequencer (and has uselessly small buffer).
They’re great chips but their documentation requires some imagination to comprehend(it’s all software api based, no hardware architecture details). I would recommend getting a chip and just trying stuff out to understand the behavior, I think the chances are high you’ll get burned someway if you try to design anything complicated ahead of time just based on what you read in the datasheet. I got burned by the buffer size differences between FT232R and FT232H which are not documented, but I guess since they make no claims I can only blame myself there.
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