| ??? 02/17/08 22:35 Read: times |
#150970 - follow up... Responding to: ???'s previous message |
Hi Jan,
Thank you so much for the informative reply. As I'm sure everyone reading this can tell, I'm no EE or CE. I'm a lowly ME trying to get this embedded stuff figured out! Yes; although the common practice is to use a pullup and use active low signalling. Then, you would not need a series resistor (which value, 1MOhm, is unusually high, btw.) You should also read the datasheet of the mcu, don't rely on datasheet of your board. Thank you for the advice. My eval. board was made by the same company who made the MCU, Analog Devices. I have been referring to all the info they provided as the datasheet because I don't know any better. :-) Re. your comment on the 1Mohm current limiting resistor I'm using. I based that on the info given in the MCU datasheet that says the maximum logic 1 input current is 10uA. I took that as a maximum rating, perhaps incorrectly, so I went with a 1MOhm to limit the input current to 5uA given a 5V Vdd. Did I misunderstand the spec? The datasheet is here: http://www.analog.com/UploadedF...DUC831.pdf (page 4) You don't need to set it before each read; it's enough to do it once at the beginning (or do nothing at all - 1 is the default state after reset), and never overwrite it into 0. Thank you again. The MCU datasheet did not say the P0 ports default to inputs. Thank you for the code help with the CFG831 SFR also! Brian |
