Trouble Getting MFM Controller to Write

As you may be aware I am trying to build an emulator for MFM disks (mainly DEC RD5x disks) using an FPGA. Things have been going moderately well in that I have managed to get the MicroVAX 2000 formatter (TEST 70) to recognise the appropriate RD5x disk by counting cylinders. However, now I am at the stage when I want the controller in the 2000 to write something. I am trying to use the formatter to write data to the disk. However, the WRITE GATE signal never gets asserted. I cannot see what is stopping the 2000 from asserting WRITE GATE. I have implemented the Index signal which looks right on the oscilloscope, and of course all the signals for track selection. I am sending dummy data on READ DATA (all logical 0s as far as I can be sure). I am as sure as I can be that I have the right pin on the connector (32 according to the 2000's tech manual). This is the output from the 2000: KA410-A RDRXfmt VSfmt_QUE_unitno (0-2) ? 0 VSfmt_STS_Siz .......... RD31 VSfmt_QUE_SerNbr (0-999999999) ? 0 VSfmt_QUE_RUsure (DUA0 1/0) ? 1 VSfmt_STS_RdMbb ..........? VSfmt_STS_FMTing .?? VSfmt_RES_ERR #3 84 FAIL Any ideas? Thanks Rob