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The number of channels in a frame must be a multiple of 2 × the number of data links.
Note:
Table 19-1 shows the number of channels each active link supports.
Table 19-1. Maximum Number of Channels Per Active Link
Number of Active Links
Maximum channel number per active link in one TDM
module
The TDM bit rate depends on:
System bus clock. The TDM processes the data in CLASS64 clock rate, so the maximum
data bit rate is limited to one half of the rate of the CLASS64 clock.
Number of active links. The total bit rate is shared by all active links, so one active link
supports the highest bit rate.
Channel width. When there are more bits per channel, there are fewer channels per
second, so higher bit rates can be processed per second.
Table 19-2 describes the maximum bit rate as a function of these parameters. Factors other than
the width of the channel can affect the bit rate, for example, the memory system load.
Channel Width (Bits)
2
4
8
16
Note:
In addition to the limits defined in Table 19-2, the maximum serial frequency is
limited to 62.5 MHz.
19.2.3 TDM Data Structures
TDM data structures are stored in transmit and receive local memory, as follows:
TDM receive local memory. Received data is stored in 256 8-byte entries located in
addresses between 0x0000–0x07FF, which is offset from the TDMx receive local memory
(see Chapter 9, Memory Map). This memory contains 1, 2, 4, 8, 16, or 32 indexed buffers
starting at 0. Each buffer contains multiple frames. The number of buffers used to store the
received data is indicated in the RNB field of the TDMx Receive Number of Buffers
Register (TDMxRNB) (discussed on page 19-68). Channel C in buffer B is the 8 bytes
starting at (256 / (RNB + 1) × B + C) × 8.
Freescale Semiconductor
Table 19-2. Factors Affecting Maximum Bit Rate
1 Active Link
CLASS64 clock/8
CLASS64 clock/4
CLASS64 clock/2
CLASS64 clock/2
MSC8144E Reference Manual, Rev. 3
1 Active Link
2 Active Links
256
128
2 Active Links
CLASS64 clock/12
CLASS64 clock/6
CLASS64 clock/3
CLASS64 clock/2
TDM Basics
4 Active Links
64
4 Active Links
CLASS64 clock/20
CLASS64 clock/10
CLASS64 clock/5
CLASS64 clock/2.5
19-13
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