Information
Universal Serial Bus Interface
MPC8308 PowerQUICC II Pro Processor Reference Manual, Rev. 1
Freescale Semiconductor 13-17
This register must be written as a DWord. Byte writes produce-undefined results. This register cannot be
written unless the USB DR controller is in the Halted state as indicated by the USBSTS[HCH]. A write to
this register while USBCMD[RS] is set produces undefined results. Writes to this register also affect the
SOF value.
In device mode, this register is read-only and the USB DR controller updates the FRINDEX[13–3] register
from the frame number indicated by the SOF marker. Whenever a SOF is received by the USB bus,
FRINDEX[13–3] is checked against the SOF marker. If FRINDEX[13–3] is different from the SOF
marker, FRINDEX[13–3] is set to the SOF value and FRINDEX[2–0] is cleared (that is, SOF for 1 msec
frame). If FRINDEX[13–3] is equal to the SOF value, FRINDEX[2–0] is incremented (that is, SOF for
125-µsec microframe).
Figure 13-11 shows the USB frame index register.
Table 13-13 shows the FRINDEX register field descriptions.
Table 13-14 illustrates values of N based on the value of the Frame List Size in the USBCMD register,
when used in host mode.
Offset 0x14C Access: Read/Write
31 14 13 0
R
— FRINDEX
W
Reset00 0 00 0 000000000000nnnnnnnnnnnnnn
Figure 13-11. USB Frame Index (FRINDEX)
Table 13-13. FRINDEX Register Field Descriptions
Bits Name Description
31–14 — Reserved, should be cleared.
13–0 FRINDEX Frame index. The value in this register increments at the end of each time frame (for example, microframe).
Bits N–3 are used for the Frame List current index. This means that each location of the frame list is
accessed 8 times (frames or microframes) before moving to the next index.
In device mode, the value is the current frame number of the last frame transmitted. It is not used as an
index.
In either mode, bits 2–0 indicate the current microframe.
Table 13-14. FRINDEX N Values
USBCMD[FS] Frame List Size FRINDEX N value
000 1024 elements (4096 bytes) 12
001 512 elements (2048 bytes) 11
010 256 elements (1024 bytes) 10
011 128 elements (512 bytes) 9
100 64 elements (256 bytes) 8
101 32 elements (128 bytes) 7