Two FV1 sharing a common EEPROM?

[knutolai]

Can 2x FV1 and 1x 24LC32A EEPROM be connected and work on the same I2C line?

I want to run a 4 channel setup where the two FV1 chips run different programs. My intention is 3 programs for each FV1. Thus the idea to have them share one EEPROM chip. If this is possible would it be an issue to change program on both FV1 chips simultaneously? (*) Both FV1 chips would be clocked by a shared external clock source (attiny84).

I read this thread btw but didn't give a clear answer IMO:
http://www.spinsemi.com/forum/viewtopic.php?f=2&t=966

(*) my idea for program selection would be a shared SPDT 3way switch for S0 and S1. FV1(A) S2 connected to 3.3v and FV1 (B) S2 connected to GND.

[frank]

Will not work, if both FV-1s change at the same time they will both try to control the EEPROM as both expect to be the only bus master and will not detect a bus contention.

Additionally as each FV-1 has an internal pull up on the lines you will not be in spec for the lines.

Use 2 EEPROMs.

[knutolai]

Thank you Frank. I'll go with 2 EEPROMs. Would there be an issue to have the S0 and S1 pins of the two FV1 chips share 1 toggle switch?

[Sweetalk]

Thank you Frank. I'll go with 2 EEPROMs. Would there be an issue to have the S0 and S1 pins of the two FV1 chips share 1 toggle switch?

That you can do. Even use a DPDT toggle switch and use one circuit for each FV1

[knutolai]

Thank you Frank. I'll go with 2 EEPROMs. Would there be an issue to have the S0 and S1 pins of the two FV1 chips share 1 toggle switch?

That you can do. Even use a DPDT toggle switch and use one circuit for each FV1

Yes a DPDT would be very safe but I'm wondering if using a SPDT would be viable. That would save PCB real estate (both the extra switch and pullup resistors).

[frank]

A SPDT 3-way (ON-OFF-ON) should work for 3 programs for 2 FV-1s. The program select inputs are very low current draw so a single pull-up should be fine for both but what you save in parts may complicate layout of the PCB.

[ice-nine]

If you are going to use a micro to control the clock, why not expand on the micro to also control the program changes, that way I think you could use one EEPROM for both FV-1's by introducing a delay into the program read of each FV-1.

[knutolai]

If you are going to use a micro to control the clock, why not expand on the micro to also control the program changes, that way I think you could use one EEPROM for both FV-1's by introducing a delay into the program read of each FV-1.

As Frank points out this will bring the I2C lines out of spec due to the internal pullups in both FV1 chips.