The 16 Axis MACRO CPU User manual has a pretty good description on page 3.
http://www.deltatau.com/manuals/pdfs/16%20AXIS%20MACRO%20CPU%20USER.pdf?id=635331532604661507
There are 72 bits of data in a MACRO packet (one 24 bit word and 3 16 bit words). The data in these words varies by control method. If you are using torque control or velocity control, for example, the 24 bit control word (from PPMAC to the MACRO CPU) contains the servo output command, and the 3rd 16 bit control word contains control bits (e.g. amp enable). The first and second 16 bit control words are unused. In this case, the 24 bit feedback word (from the MACRO CPU to PPMAC) contains the ECT data, and the 3rd 16 bit feedback word contains status data (e.g. amp fault). In the case of direct PWM over MACRO, all registers are used (with PWM commands for each phase in the first three command words, and command data in the final word, and ECT data, ADC A, ADC B, Status occupying the feedback words).
The breakdown of what bits go where in the flag registers can be found in the Turbo SRM "MACRO Flag Registers" section.
http://www.deltatau.com/manuals/pdfs/TURBO%20SRM.pdf?id=635331532581848423
REMEMBER - in Power PMAC, the Bits are in the Upper 24 (or 16) bits of the 32 bit word, so you will have to +8 on the bit numbers.