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Robert Pearce

Can I use a JTAG-SMT2-NC to program an I2C EEPROM ?

Question

I have designed a board to program serial flash memories using the JTAG-SMT2-NC operated as an SPI master.

This works fine but now I want to use the same board to program an I2C EEPROM (on a different target).

FTDI's document "USB to I2C Example using the FT232H and FT201X devices" suggests that this should be possible and I belive that the JTAG-SMT2-NC  uses the FT232H.

Has anyone tried this?

What would the mapping of the connections be?  I imagine that it would be:-

TMS - connect to Write Protect on the EEPROM

TCK - connect to I2C's SCK

TDI, TDO - tie together and connec to I2C's SDA

alternatively I suppose that one could bit-bash the GPIO pins (GPIO0, GPIO1, and GPIO2) but this would require a hardware change to my adapter that I'd prefer to avoid.

 

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Hi @Robert Pearce,

I reached out to our design engineer about your thread and they responded with "I2C is an open collector protocol. The SMT2 uses push-pull drivers, and not open drain buffers on TMS, TDI, and TCK. Each of those buffers are tri-state buffers and they do have individual enable pins hooked up to the FTDI chip so it may be possible to do this by tieing TDI and TDO together. However, it’s going to require a lot of manual shift operations operations to implement it because of the ACK bit. Additionally, they are going to have to be real careful to ensure that the enable pins of the buffers are driven to the correct state at the correct time. They will also need external pull-ups, as 100K isn’t going to cut it. There is no Adept SDK API that will let you drive the SMT2 pins in the manner required for I2C so this will have to be done using D2XX API’s directly.
 
I think it would be a lot easier to use an SPI ROM since the SMT2 supports that protocol."

thank you,

Jon

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