MPC8250 MCC operating on 2-bit channels

Stevan Ignjatovic stevan at
Wed Sep 21 01:16:48 EST 2005


My problem is concerned with the multi channel controller MCC2 on
MPC8250. Its task is to relay messages from D channels between Local
Exchange and ISDN BRA subscribers. All active D channels (up to 128) are
aggregated into single stream tied directly to the TDMc2, ie. both
TDMc2_Rx and TDMc2_Tx are divided into 2-bit channels. 2.048MHz clock
and 8KHz frame pulse are generated externaly and are connected to
corresponding processor pins (common pins for receive and transmit

When tested with internal loopback (SI2MR[SDM2]=0b10) everything works
fine, ie. for example the message we send through channel 0 is received
correctly on channel 0. However, it doesn't work in real application.

The debugging process led me to this simple test. I connected TDMc2_Rx
and TDMc2_Tx to FPGA in which I implemented the delay of N frames (N x
125us, since the frame pulse is 8KHz), such that for N=0 I have simple
external loopback, for N=1 delay of one entire frame, and so on. I was
sending messages through channel 0 (it is the only channel I actually
started). The results I obtained were very strange. For N=0, N=4, N=8
the received message was correct, but for N=1,2,3 it was not (I was
usually reported CRC erro,r or non octet alignment error, or abort).When
I tried with 4-bit channels, the result was correct for N=0,2,4,....
Only with 8-bit channels I obtained correct result for all frame delays.
The fact that everything works fine with 8-bit channels makes me believe
that all MCC and SIRAM settings are ok. I tried many combinations of
SIRAM programming (For example, I tried to program only channel 0 as
2-bit and all others as 8-bit, or as null entries), but it didn't work
out. It is also worth to mention that I have never received GUN or GOV

Has anybody dealt with 2-bit channels on MCC? What can cause such
problems (remember that everything works fine with 8-bit channels). I
would also appreciate if somebody has the possibility to implement
similar test.


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