Universal Serial Bus (USB)
MCF5272 ColdFire Integrated Microprocessor User’s Manual, Rev. 3
Freescale Semiconductor
12-9
12.3.2
Register Descriptions
The following are detailed register diagrams and field descriptions.
12.3.2.1
USB Frame Number Register (FNR)
Once every 1 ms, the USB host issues a start-of-frame packet containing a frame number. The FNR register
Figure 12-3. USB Frame Number Register (FNR)
12.3.2.2
USB Frame Number Match Register (FNMR)
FNMR is used to signal, via the FRM_MAT interrupt, when a particular frame number is issued by the
USB host. To avoid a false match during intermediate states of a byte write operation to the FNMR,
Figure 12-4, byte accesses to this register are not supported and cause an access error.
Figure 12-4. USB Frame Number Match Register (FNMR)
15
11
10
0
Field
—
FRM
Reset
0000_0000_0000_0000
R/W
Read
Addr
MBAR + 0x1002
Table 12-3. FNR Field Descriptions
Bits
Name
Description
15–11
—
Reserved, should be cleared.
10–0
FRM
USB frame number. Contains the current USB frame number. FRM is updated with the new frame number
each time the device successfully receives a start-of-frame (SOF) packet from the USB host. The new frame
number is contained in the SOF packet.
15
11
10
0
Field
—
FRM_MAT
Reset
0000_0000_0000_0000
R/W
Addr
MBAR + 0x1006
Table 12-4. FNMR Field Descriptions
Bits
Name
Description
15–11
—
Reserved, should be cleared
10–0
FRM_MAT
Frame number match value. Contains the USB frame number match value. When the FNR value equals
the value in the register, a FRM_MAT interrupt is generated.