32xan

Actually, that isn't working. I made that mistake myself once, when PxREN is enabled, PxDIR does not switch it from hard to soft driving, but rather switched PxIN to read from PxOUT or from the actual pin.
To switch between pull-down and drive low you'd need to set PxOUT to 0, PxDIR to 1 and control using PxREN (1=pull-down/release, 0=drive low).
When switching to read mode (when receiving the ack bit and responses) switch PxDIR to 0 to let PxIN read the actual pin state, you cannot drive the pin low while PxDIR is 0, so switch back to 1 to enable driving the pin again.

Yeah the closest you can get to open-drain is disable the pullup/pulldown (PxREN), set the PxOUT bit for those ports to 0, then control the port using PxDIR (1=pull it hard low, 0=release)
 
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The open-drain mode is not available outside of the USI/USCI mode. Only option is to put the pin in input mode, where it tri-states has high impedance, allowing the pull up to work.

Capacitor is missing on the Reset pin of MSP430.
 
Also, the TLC5916 has min 0.6V on the Vo for 26 mA (from datasheet). With only 0.4V on the Vo of the TLC5914 I kind of curios how stable/predictable it would sink 10mA (or whatever you would programm TLC5914 to sink)?