PEB20560 Datasheet, PDF (222/433 Pages) Infineon Technologies AG – ICs for Communications

PEB 20560
Operational Description
3.1.5.2 SACCO-A Reception
Subscribers who are to participate in the D-channel arbitration for the SACCO-A must
send “all 1s” as inter frame timefill of their D-channels. Flags or idle codes other than
“all 1s” are not permitted as inter frame timefill. For any participating subscriber, the
“blocked” code must be programmed into the downstream Control Memory (CM). Also,
the subscriber’s D-channel must be enabled in the DCE-register.
In the full selection state, the D-channel arbiter overwrites the downstream “blocked”
code of enabled subscribers with the “available” code. On the upstream CFI-input lines,
the D-channel arbiter monitors all D-channels enabled in the DCE-registers.
When the D-channel arbiter detects a ‘0’ on any monitored D-channel it assumes this to
be the start of an opening flag. It therefore strobes the D-channel data of this subscriber
to the SACCO-A and starts the Suspend Counter. For this selected subscriber, the
D-channel arbiter continues to overwrite the downstream “blocked” code with the
“available” code. However, all other enabled subscribers are now passed the “blocked”
code from the downstream CM.
If the SACCO-A does indeed receive an HDLC-frame – complete or aborted – from the
selected subscriber, the Suspend Counter is reset. While the SACCO-A receives data
from the selected subscriber, the “blocked” code stops all other subscribers from sending
data to the SACCO-A. After the SACCO-A has received a closing flag or abort sequence
for the subscribers frame, the D-channel arbiter stops strobing the subscriber’s data to
the SACCO-A and enters the limited selection state.
If, after the initial ‘0’, the SACCO-A does not receive an HDLC-frame – complete or
aborted – from the selected subscriber, it does not reset the Suspend Counter.
Eventually, the Suspend Counter under flows, setting off the ISTA.IDA-interrupt. The
subscriber who sent the erroneous ‘0’ can then be identified in the ASTATE-register. Any
subscriber who frequently sends erroneous ‘0’s should be disabled from the DCE, and
the cause of the error investigated. After the ISTA.IDA-interrupt, the SACCO-A receiver
must be reset to resume operation in the full selection state.
The limited selection state is identical to the full selection state, except that the
subscriber who last sent data to the SACCO-A is excluded from the arbitration. This
prevents any single subscriber from constantly keeping the SACCO-A busy. The
“blocked” code of the CM is passed to the excluded subscriber, while the D-channel
arbiter sends all other enabled subscribers the “available” code. All enabled subscribers
– except the one excluded – are monitored for the starting ‘0’ of an opening flag. How
long the exclusion lasts can be programmed in the AMO-register. If none of the
monitored subscribers has started sending data during this time, the D-channel Arbiter
re-enters the full selection state.
Semiconductor Group
3-16
2003-08