peb3456 Infineon Technologies Corporation, peb3456 Datasheet - Page 70

• Manufacturer Part Number: peb3456
• Description: Channelized T3 Termination With Ds3 Framer, M13 Multiplexer, T1/ E1 Framers And 256 Channel Hdlc/ppp Controller
• Manufacturer: Infineon Technologies Corporation

PEB 3456 E
Functional Description
field of the transmit descriptor and to compare this with the number of bytes requested
by the transmit buffer.
Depending on the bit field NO in the transmit descriptor several read accesses must be
performed by the data management unit. It stops serving the request as soon as the
requested amount of data was transferred to the transmit buffer, when a Frame End bit
(FE) in the processed transmit descriptor is set or when the channel was aborted using
a ‘Transmit Abort’ command. Serving the request can also be suspended, when the
programmed transmit burst length (CONF3.TPBL) is reached. All these events may
result in open transmit buffer locations, but the data management unit stores this
information as open requests in the channel database and processes these requests
continuously.
The data management unit alternately serves requests issued by the transmit buffer or
open requests stored in its internal channel database. If there are open requests for a
channel, data transmission will be initiated. The procedure is the same as described
above. It stops, if the requested amount of data is served or when the FE bit field is set.
If a transmit descriptor has its FE bit set and all data of the data section is moved to the
transmit buffer, the data management unit serves requests of further channels or looks
for open requests in its database. Therefore open requests from other channels are
served faster and possible underruns can be avoided. The next transmit descriptor will
be retrieved with the next data transfer of the channel.
When the data management unit completed reading a data section associated with a
transmit descriptor, it updates the complete (C) bit in the status word of the transmit
descriptor if the complete enable (CEN) bit is set. Additionally a ’Transmit Host Initiated’
interrupt vector is generated if the THI bit is set in the transmit descriptor. Afterwards the
data management unit the TE3-CHATT branches to the next transmit descriptor.
Descriptor hold operation
The data transfer is controlled by the HOLD bit, which is located in the first DWORD of
a transmit descriptor. The HOLD bit indicates that the marked descriptor is the last
descriptor in a linked list. The data management unit will not branch to the next descriptor
until the hold condition is removed or a ’Transmit Abort’ command forces the TE3-
CHATT to branch to a new linked list.
If the HOLD bit and the frame end bit are set together in a descriptor, the data
management unit transfers all data of the belonging data section to the transmit buffer
and optionally sets the C-bit in the current transmit descriptor. When a new data transfer
is requested (either from the transmit buffer or an open request) the data management
unit repolls the descriptor. If the HOLD bit is removed, it will branch to the next transmit
descriptor. If the HOLD bit is still set, that channel is suspended for further operation.
Following requests from the transmit buffer will not be served, but the number of
requested data is stored in the open request registers.
Data Sheet
70
05.2001