Semiconductor Group
6-47
1999-04-01
On-Chip Peripheral Components
C541U
If the number of data bytes to be transferred is greater than the maximum packet size (given by
MaxLen), the data is split up automatically into packets, which are transferred one after the other.
Figure 6-30 gives an example of an USB read access, where data from the CPU is split up into two
packets. When MaxLen is reached during the CPU write access, the currently active buffer is
switched to USB side (UBF=1). The CPU continues writing data to the buffer. When the complete
data packet has been written to the buffer by the CPU, bit DONE is set by software to indicate the
end of the data packet (CBF=1). In the example, the USB buffer has not been read out. It is still full
for the USB and can not be swapped (CBF=UBF=1). When the USB read access has occured
(CBF=0), the buffers are automatically swapped and bit SOD is set.
Figure 6-30
Double Buffer Mode USB Read Access: Data Length greater than Packet Length (MaxLen)
Frame n
Frame n+1
Time
SOF (n)
set
Number of
Data Bytes
MaxLen
USB read accesses
CPU write accesses
MCT03410
SOF (n+2)
set
Time
SOF (n+1)
set
1
Page 1
Page 1
Swap
Buffer
Swap
Buffer
UBF
= 0
USB Buffer
CPU Buffer
CBF
= 0
MaxLen
Page 0
Page 1
Page 0
Page 0
UBF = 1
UBF = 1
EOD = 1
SOD = 1
DONE = 1
CBF = 1
Summary of Contents for C541U
Page 1: ... 8 LW 026 0LFURFRQWUROOHU 8VHU V 0DQXDO http www siem ens d Sem iconductor ...
Page 7: ......
Page 21: ...Semiconductor Group 2 6 1997 10 01 Fundamental Structure C541U ...
Page 37: ...Semiconductor Group 4 6 1997 10 01 External Bus Interface C541U ...
Page 133: ...Semiconductor Group 6 88 1999 04 01 On Chip Peripheral Components C541U ...
Page 163: ...Semiconductor Group 8 8 1997 10 01 Fail Safe Mechanisms C541U ...
Page 185: ...Semiconductor Group 10 14 1997 10 01 OTP Memory Operation C541U ...