C8051F321-GMR Datasheet, PDF (142/250 Pages) Silicon Laboratories – Full Speed USB, 16 k ISP FLASH MCU Family

C8051F320/1
15.3. USB Register Access
The USB0 controller registers listed in Table 15.2 are accessed through two SFRs: USB0 Address
(USB0ADR) and USB0 Data (USB0DAT). The USB0ADR register selects which USB register is targeted
by reads/writes of the USB0DAT register. See Figure 15.2.
Endpoint control/status registers are accessed by first writing the USB register INDEX with the target end-
point number. Once the target endpoint number is written to the INDEX register, the control/status registers
associated with the target endpoint may be accessed. See the “Indexed Registers” section of Table 15.2
for a list of endpoint control/status registers.
Note: The USB clock must be active when accessing USB registers.
8051
SFRs
USB0DAT
USB Controller
Interrupt
Registers
FIFO
Access
Common
Registers
Index
Register
USB0ADR
Endpoint0 Control/
Status Registers
Endpoint1 Control/
Status Registers
Endpoint2 Control/
Status Registers
Endpoint3 Control/
Status Registers
Figure 15.2. USB0 Register Access Scheme
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Rev. 1.4