Motorola PowerQUICC II MPC8280 Series Reference Manual page 1177

The following figures provide examples of partial fill mode operation:
1. Five packets fit exactly within the PFT limit
Cell AAL2
header STF packet 1
0
2. Because PFT is less than the combined lengths of packet 1, packet 2 and packet 3,
the ATM cell is sent only with packets 1 and 2. (Packet 3 will be sent with the next cell.)
Cell AAL2
header STF packet 1
0
Cell AAL2
header STF packet 1
0
3. Because the first packet exceeds the PFT value, the CPS-PDU consists only of this packet
(and the unused octets are padded with zeros).
Cell
header STF
0
33.3.4 No STF Mode
The no-STF (no start of frame) mode enables the transmission of 48-byte packets by not
including the STF byte in the CPS PDU. The no-STF mode should always be used with PFT
programmed to 47 in order to prevent split and partial packets. For the AAL2 channels that
use this mode, packets must not be larger than a maximum packet size of 48.
The user activates this mode per ATM channel by doing the following:
1. Setting TCT[NoSTF]=1 and TCT[PFM]=1
2. Establishing a partial fill threshold by programming TCT[PFT]=47
The following figure shows a cell using no-STF mode:
Cell
header
0
MOTOROLA
Freescale Semiconductor, Inc.
AAL2 AAL2
packet 2 packet 3
AAL2 AAL2
packet 2 packet 3
Remove packet 3 PFT
AAL2
packet 2
PFT
AAL2
packet 1
PFT
AAL2 packet of 48 bytes
Chapter 33. ATM AAL2
For More Information On This Product,
Go to: www.freescale.com
AAL2 AAL2
packet 4 packet 5 Padding
PFT
Empty
Padding
Padding
AAL2 Transmitter
Transmit
Transmit
Transmit
33-9