If you check out the datasheet (page 28 Table 25) it shows that you have to physically set the sync_out or sync_in bits to get any response on pin 12.
In other words it's not a problem pulling it to VSS 8)
I've been working on this chip through an 18F4550 PIC for the last few days and have just added a 512Kbit EEPROM to swap out the frame data. The EEPROM holds 38 full datasets and you can flip the data on the fly.
Great fun this ain't it.... 