Memory Map/Register Definition
MCF548x Reference Manual, Rev. 3
Freescale Semiconductor 29-11

Table 29-3. USBCR Field Descriptions

Bits Name Description
31–6 — Reserved, should be cleared.
5 RAMSPLIT RAM split. The endpoint FIFO RAM can be configured for maximum flexibility or for maximum
performance. The individual FIFO base and depth values (in the EPnFRCFGR) should be carefully
programmed taking into account the respective direction (IN/OUT) of each FIFO and the value of this
control register. Care should be taken not to program those values such that the space required
exceeds the FIFO space available to the IN/OUT endpoints.
Setting this bit configures the endpoint FIFO RAM for maximum performance by splitting the total
endpoint FIFO RAM space in half, dedicating half to be shared by all IN endpoints and the other half
to be shared by all OUT endpoints. In this configuration, both the USB module and the
application/DMA can receive/transmit the endpoint FIFO data without incurring wait states due to
FIFO RAM arbitration.
If set, special care must be taken with the bi-directional control endpoint, endpoint 0. In this case,
software must configure space in both the Rx and Tx RAM regions for the control EP since it is
bi-directional depending on the request type. Furthermore, if the seperate regions within the Rx and
Tx RAM spaces do not have the same base address and byte depth for EP0, the software must be
sure to set the EP0FRCFGR[BASE] and EP0FRCFGR[DEPTH] values appropriately before
servicing a Control read/write request.
Clearing this bit configures the endpoint FIFO RAM for maximum flexibility at the cost of
performance. In this configuration, the entire endpoint FIFO RAM space can be shared by all
endpoints. However, application/DMA accesses will incur wait states when accessing the endpoint
FIFO data at the same time that the USB is receiving/transmitting data.
0 The endpoint FIFO RAM is configured for maximum flexibility.
1 The endpoint FIFO RAM is configured for maximum performance.
4 — Reserved, should be cleared.
3 RAMEN Descriptor RAM Enable. This bit determines the accessibility of the descriptor RAM contents.
0 The application can read/write the descriptor RAM via the DRAMDR register. The device cannot
access the descriptor RAM contents.
1 The USB device controller can read the descriptor RAM as controlled by the DRAMCR register.
The user cannot access the descriptor RAM contents.
2 RST USB reset. This bit executes a hard reset of the USB module. This bit allows the system software to
force a reset of the USB’s logic when the system is first connected to the USB, or for debug
purposes.