PCA9501 Addressing (Newbie)

sparky88

·I am having trouble addressing my PCA9501 I/O expander chip.· I can't seem to access the I/O pins.· I have had success with PCF8574A, but no luck with PCA9501.· I'm using the right voltage (3.3v) and pull·up resistors (1.6K)for·SDA and SCL ( as per the data sheet) but I can' get the I/O pins to go low. All addressing pins are grounded.
Thanks for any help.

'{$STAMP BS2p}

·X CON 500
·ADDRESS CON %0000000
·MAIN:
·I2COUT 0, ADDRESS,[noparse][[/noparse]%00000000]
·· PAUSE· X
·I2COUT 0, ADDRESS,[noparse][[/noparse]%11111111]
·· PAUSE· X
·GOTO MAIN:

Newzed

The pins won't go low by themselves.· You have to pull them low.

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Sid Weaver
Try the Stamp Tester

http://hometown.aol.com/newzed/index.html
·

Jon Williams

Sometimes those "single register" devices have an internal buffer. Modify your program to write each new value twice so that the second write actually pushes the first from the buffer to the output.

I2COUT 0, slvAddr, [noparse][[/noparse]%00000000, %00000000]
PAUSE 500
I2COUT 0, slvAddr, [noparse][[/noparse]%11111111, %11111111]
PAUSE 500

The data shee shows a FET between each IO pin and Vss, so I don't think you have to pull the outputs low. In fact, the data shee suggests you pull then high if you're going to use them as inputs.

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Jon Williams
Applications Engineer, Parallax
Dallas Office