HFC-SUSB Cologne Chip AG, HFC-SUSB Datasheet - Page 31

• Manufacturer Part Number: HFC-SUSB
• Description: Isdn S/t HDLC Basic Rate Controller
• Manufacturer: Cologne Chip AG

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3.4.2.2 FIFO control bytes for transmit FIFOs
For the transmit FIFOs (OUT transfer on enpoints 1..4 or 5..8) the first data byte of the first data packet
of a transfer is used as FIFO control byte (see Table 4 and Figure 5). The host must indicate the end of a
HDLC frame in this FIFO control byte if the HDLC frame ends after this transfer.
Bit
Name
Bit Name
EoF
Table 4: FIFO control byte for transmit FIFOs
The HFC-S USB assumes a data transfer as finished if the data packet size is less than wMaxPacketSize
(see also USB_SIZE register).
Figure 5 shows how a complete HDLC frame can be transmitted to the HFC-S USB. The EoF-bit in the
FIFO control byte must be set to '1' if the HDLC transmit frame ends after the USB transfer. If the last
data packet has the same length as wMaxPacketSize an empty data packet must be sent next. Otherwise
the HFC-S USB would assume the data transfer (and the HDLC frame) as not yet finished.
As you can see in the figure above the FIFO control byte is only required in the first data packet of a
transfer.
Figure 5: FIFO control byte for transmit FIFOs
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*
The wMaxPacketSize in the USB endpoint descriptors must be the same as the size selected in the
USB_SIZE register (or USB_SIZE_I register for isochronous transfers).
important!
7
FIFO Control Byte for Transmit FIFOs (Host Transmits Data)
Description
In transparent mode this bit must be '0'.
'1'
6
end of HDLC frame after data transfer
5
unused
4
3
2
1
Cologne
Chip
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EoF
0