mcf5272 Freescale Semiconductor, Inc, mcf5272 Datasheet - Page 288

• Manufacturer Part Number: mcf5272
• Description: Mcf5272 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

Software Architecture and Application Notes
12.3.4 USB Module Access Times
The access times for the USB module depend on whether the access is to a register, to an
endpoint FIFO (EPnDR register), or to the configuration RAM.
12.3.4.1 Registers
The USB module registers are accessed through the internal S-bus. Each register access
takes 3 clock cycles for reads and writes.
12.3.4.2 Endpoint FIFOs
The FIFO access time depends on the size, the time between accesses, and whether the
previous FIFO access was for the same endpoint. After a longword access to an endpoint’s
FIFO, the next longword in the FIFO is cached for a quicker access time on the next
longword read. This mechanism is reset every time another endpoint is accessed.
Table 12-19 shows the access times for the FIFOs.
12.3.4.3 Configuration RAM
The configuration RAM is longword accessible only. Access times for reads from the
configuration RAM are eight clock cycles per access. Clock cycle access times for
back-to-back writes to the configuration RAM are 3-5-5-5-5-5... Access times for writes
separated by at least 1 clock cycle are 3-3-3-3-3-3…
12.4 Software Architecture and Application Notes
This section describes architecture and applications.
12.4.1 USB Module Initialization
At power-up, the USB module should be initialized within 20 ms if the USB port is
connected. This time corresponds to the 10 ms reset signaling and 10 ms reset recovery time
when a device is detected. The following steps are necessary to initialize the USB module
for operation:
12-28
Byte
Word
Long (back to back)
Long (1 clock gap)
Long (2 clock gap)
Long (3+ clock gap)
Access Type
Table 12-19. USB FIFO Access Timing
MCF5272 User’s Manual
5
6
8-4-6-6-6-6...
8-3-5-5-5-5...
8-3-4-4-4-4...
8-3-3-3-3-3...
Read
4
4
4-6-6-6-6-6...
4-5-5-5-5-5...
4-4-4-4-4-4...
4-4-4-4-4-4...
Write
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