Hello again,
I recently started a new thread about interfacing a PCF8574 with transistors to control solenoid valves (see here: http://forum.allaboutcircuits.com/showthread.php?t=87803)
So far so good. Throughout the thread I explained that I chose to use a PCA9534A portextender (http://www.ti.com/lit/ds/symlink/pca9534a.pdf)
Now, I hooked up the device and without doing anything to it (meaning writing any commands over the I2C bus to the device) all output pins should be pulled to 5 V, correct (datasheet states on page 8 that power on reset all pins will be pulled to 1 meaning 5 V if I interpreted the datasheet correctly) ?
What I observe now is that the pins have around 2 V and I was wondering if somebody could explain what I am doing wrong, if I am doing something wrong ?
Some more infos about the connections of the chip:
- Pin 8 is connected to ground
- Pin 16 is connected to 5 V
- all address pins are pulled to ground and the output pins are connected to various devices (4050 level shifter and transistors)
- INT pin is not connected
On the TI website one can find an errata to the datasheet of the chip (http://www.ti.com/lit/er/scpz012/scpz012.pdf) which talks about the power on reset and that if the specifications are not met then the chip goes into some kind of locked state. I was wondering if that could be the issue that I couldn't read the 5 V on the output pins on power up ?
Or could it be the issue that in the control register all bits are pulled to 1 which defines the ouput pins as inputs (compare page 8 on datasheet, table 5, power up default for the control register) ?
As always any help is greatly appreciated.
Thanks,
mvschaefer
PS: If I have forgotten to supply any infos necessary to wrap ones head around the issue then I would be more than happy to supply it.
http://forum.allaboutcircuits.com/showthread.php?t=87803
I recently started a new thread about interfacing a PCF8574 with transistors to control solenoid valves (see here: http://forum.allaboutcircuits.com/showthread.php?t=87803)
So far so good. Throughout the thread I explained that I chose to use a PCA9534A portextender (http://www.ti.com/lit/ds/symlink/pca9534a.pdf)
Now, I hooked up the device and without doing anything to it (meaning writing any commands over the I2C bus to the device) all output pins should be pulled to 5 V, correct (datasheet states on page 8 that power on reset all pins will be pulled to 1 meaning 5 V if I interpreted the datasheet correctly) ?
What I observe now is that the pins have around 2 V and I was wondering if somebody could explain what I am doing wrong, if I am doing something wrong ?
Some more infos about the connections of the chip:
- Pin 8 is connected to ground
- Pin 16 is connected to 5 V
- all address pins are pulled to ground and the output pins are connected to various devices (4050 level shifter and transistors)
- INT pin is not connected
On the TI website one can find an errata to the datasheet of the chip (http://www.ti.com/lit/er/scpz012/scpz012.pdf) which talks about the power on reset and that if the specifications are not met then the chip goes into some kind of locked state. I was wondering if that could be the issue that I couldn't read the 5 V on the output pins on power up ?
Or could it be the issue that in the control register all bits are pulled to 1 which defines the ouput pins as inputs (compare page 8 on datasheet, table 5, power up default for the control register) ?
As always any help is greatly appreciated.
Thanks,
mvschaefer
PS: If I have forgotten to supply any infos necessary to wrap ones head around the issue then I would be more than happy to supply it.
http://forum.allaboutcircuits.com/showthread.php?t=87803