![](http://datasheet.mmic.net.cn/330000/PEF20321_datasheet_16444041/PEF20321_60.png)
PEB 20321
PEF 20321
Basic Functional Principles
Data Sheet
60
2001-02-14
The shared memory allocated for each TX and Rx channel is organized as a chaining
list of buffers set up by the host. Each chaining list is composed of descriptors and data
sections. The descriptor contains the pointer to the next descriptor, the start address and
the size of a data section. It also includes control information like frame end indication,
transmission hold and rate adaption with interframe time-fill.
In the transmit direction the MUNICH32X reads a Tx descriptor, calculates the data
address, writes the current Tx descriptor address into the CCB, and fills the on-chip
Tx buffer. When the data transfer of the specified section is completed, the MUNICH32X
releases the buffer, and branches to the next Tx descriptor.
If a frame end is indicated, the HDLC, TMB or TMR frame will be terminated and a
specified number of the interframe time-fill bytes will be sent in order to perform rate
adaption.
If frame end is found in a Tx descriptor of a TMA channel, the specified number of
programmable TMA flags is appended to the data in the descriptor.
If frame end is found in a Tx descriptor of a V.110/X.30 channel, the frame is aborted
(after the data in the descriptor are sent) by finishing the current 10-octet frame with
‘
zeros
’
and sending 2 more 10-octet frames with
‘
zeros
’
which leads to a loss of
synchronism on the peer side. An adjustment for the inserted zeros in HDLC is
programmable, which leads to a reduction of the specified number of interframe time-fill
by
1
/
8
th
of the number of zero insertions. This can be used to send long HDLC frames
with a more or less fixed data rate in spite of the zero insertions. A maskable interrupt is
generated before transmission is started again.