
CHAPTER 14 USBU (UNIVERSAL SERIAL BUS UNIT)
User’s Manual U14579EJ2V0UM
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14.4.10 IsochronousTD fields
Table 14-5 shows details about the IsochronousTD fields.
Table 14-5. IsochronousTD Fields
Field Name
R/W
Function
SF
R
Starting Frame
Lower 16 bits of the frame number that is sent by the first data packet of the IsochronousTD
DI
R
Delay Interrupt
Time until an interrupt request is issued after this IsochronousTD processing is completed
FC
R
Frame Count
Number of data packets indicated by this IsochronousTD. When this area is 0, it indicates that one
data packet is included. When it is 7, it indicates that eight data packets are included.
CC
R/W
Condition Code
When an IsochronousTD is moved to the Done queue (transfer completed queue), this area
contains the completion code.
BP0
R
Buffer Page 0
This area displays the physical page number of the first byte of the data buffer used by this
IsochronousTD.
NextTD
R/W
Next TD
This area indicates the next IsochronousTD in the IsochronousTD queue that is liked with the ED.
BE
R
Buffer End
This area contains the physical address of the last byte of the buffer.
OffsetN
R
Offset N (N = 0 to 7)
This area is used for determining the size and starting address of the isochronous data packet.
PSWN
W
Packet Status Word N (N = 0 to 7)
This area contains the completion code and the data size that was received by the isochronous
data packet.
RFU
R
Reserved for Future Use
Reserved. Write 0 to these bits. 0 is returned after a read.
An IsochronousTD has (FC area value + 1) frame buffers, within the range from 1 to 8. The first data packet is sent
by the frame for which the lower 16 bits of the HcFmNumber register matches the SF area of the IsochronousTD. If the
buffer address exceeds the 4 KB boundary during a data packet transfer, the higher 20 bits of the BE area are used as
the physical address of the next buffer. Therefore, the next buffer address will be byte 0 of the same 4 KB page space
as the one where the last byte is maintained.
14.4.11 HCCA (Host Controller Communication Area)
The HCCA (Host Controller Communication Area) is a 256-byte area of system memory, which is used by system
software for transmitting specific control/status information to or receiving this information from the HC. The system
software always writes this area address in the HcHCCA register of the HC.