MPC8280 datasheet(838/1386 Pages) FREESCALE

838 / 1386 page

Universal Serial Bus Controller

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

27-22

Freescale Semiconductor

Table 27-14 describes USBS fields.

27.5.7.8

USB Start of Frame Timer (USSFT)

NOTE

The USSFT described in this section is available only on .13

µm (HiP7)

Revision A.0 and future devices.

When enabled by USMOD[SFTE], the USSFT contains the current time within the frame with a resolution

of one bit time. When the value of USSFT wraps from 11,999 to 0, a CP interrupt is asserted to trigger the

transmission of a SOF packet, and USBER[SFT] is set

The USSFT may be read at any time.

Table 27-13 describes USSFT fields.

27.6

USB Buffer Descriptor Ring

The data associated with the USB channel is stored in buffers that are referenced by BDs organized in BD

rings located in the dual-port RAM (refer to Figure 27-17). These rings have the same basic configuration

as those used by the SCCs and SMCs.

There are up to four separate transmit BD rings and four separate receive BD rings, one for each endpoint.

The BD ring allows the user to define buffers for transmission and buffers for reception. Each BD ring

forms a circular queue. The CP confirms reception and transmission or indicates error conditions using the

BDs to inform the processor that the buffers have been serviced.

Table 27-14. USBS Fields

Bit

Name

Description

0–6

—

Reserved

IDLE

Idle status. IDLE is set when an idle condition is detected on the USB lines, it is cleared when

the bus is not idle.

012

Field

SFT

Reset

0010_1110_1101_1000

R/W

Addr

0x11B78

Figure 27-16. USB Start of Frame Timer (USSFT)

Table 27-15. USSFT Fields

Bit

Name

Description

0–1

—

Reserved, should be cleared.

2–15

SFT

Start of Frame Time. This field contains the number of bit times since the last SOF trigger.

Note that the actual SOF transmission occurs slightly later.

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