Advance Information
When the input frame offset is enabled, an "internal
delay" of up to four clock periods is added to the
actual data input sampling, providing the MT89L86
serial timing unit a new input frame reference. An
internal virtual frame is created which is aligned with
the framing of the actual serial data coming in at the
serial inputs and not with the FR frame pulse input.
In this operation, the transmission of the output
frame on the serial links is still aligned to the frame
pulse input signal (FR).
The selection of the data input sampling delay is
defined by the CPU in the Frame Input Offset
Register (FIO). If this function is not required in the
user's applications, the FIO register should be set up
during system initialization to a state where offset
functions are disabled.
MT89L86
throughput delay capabilities on a per-channel basis.
For voice applications, variable throughput delay can
be selected ensuring minimum delay between input
and output data. In wideband data applications,
constant throughput delay can be selected
maintaining the frame integrity of the information
through the switch.
The delay through the device varies according to the
type of throughput delay selected in the V/C bit of the
connect memory high.
Variable Throughput Delay Mode (V/C bit = 0)
Identical I/O Data Rates
The delay in this mode is dependent on the
combination of source and destination channels and
it is independent of the input and output streams.
The minimum delay achievable in this MT89L86
depends on the data rate selected for the serial
streams. For instance, for the 2.048 Mb/s data rate,
the minimum delay achieved corresponds to three
time-slots. For the 4.096 Mb/s data rate it
corresponds to five time-slots while it is nine time-
slots for the 8.192 Mb/s data rate. Switching
Delay Through the MT89L86
The switching of information from the input serial
streams to the output serial streams results in a
delay. Depending on the type of information to be
switched, this MT89L86 can be programmed to
perform time-slot interchange functions with different
Output Channel (# m)
Input Rate
m<n
2.048 Mb/s
4.096 Mb/s
8.192 Mb/s
32-(n-m) t.s.
64-(n-m) t.s.
128-(n-m) t.s.
m=n, n+1, n+2
m-n + 32 t.s.
m-n + 64 t.s.
m-n + 128 t.s.
m= n+3, n+4
m-n t.s.
m-n+64 t.s.
m-n+128 t.s.
m=n+5, .. n+8
m-n t.s.
m-n t.s.
m-n+128 t.s.
m > n+8
m-n t.s.
m-n t.s.
m-n t.s.
Table 3a - Variable Throughput Delay Values for Identical I/O Rate Applications
n= input channel, t.s. = time-slot
I/O Data Rate
Configuration
2 Mb/s to 4 Mb/s
2 Mb/s to 8 Mb/s
4 Mb/s to 2 Mb/s
8 Mb/s to 2 Mb/s
Output Stream Used
0, 1
dmin=5x 4Mb/s t.s.
dmax=1 fr.+(4x 4Mb/s t.s.)
dmin=9x 8Mb/s t.s.
dmax=1 fr.+(8x 8Mb/s t.s.)
dmin=3x 2Mb/s t.s.
dmax=1 fr.+(2x 2Mb/s t.s.)
dmin=3x 2Mb/s t.s.
dmax=1 fr.+(2x 2Mb/s
t.s.)
dmin=(2x 2Mb/s t.s.)+
(3x 8Mb/s t.s.)
dmax=1 fr.+(1x 2Mb/s
t.s.)+(3x 8Mb/s t.s.)
dmin=(2x 2Mb/s t.s.)+(1x 4Mb/s t.s.)
dmax=1 fr.+(1x 2Mb/s t.s.)+(1x 4Mb/s t.s.)
dmin=(2x 2Mb/s t.s.)+
(2x 8Mb/s t.s.)
dmax=1 fr.+(1x 2Mb/s
t.s.)+(2x 8Mb/s t.s.)
dmin=(2x 2Mb/s t.s.)+
(1x 8Mb/s t.s.)
dmax=1 fr.+(1x 2Mb/s
t.s.)+(1x 8Mb/s t.s.)
2, 3
4, 5
6, 7
Table 3b - Min/Max Throughput Delay Values for Different I/O Rate Applications
Notes:
dmin and dmax are measured in time-slots and at the point in time when the output channel is completely shifted out.
t.s. = time-slot
fr. = 125
µs
frame
2 Mb/s t.s. = 3.9
µs
4 Mb/s t.s. = 1.95
µs
8 Mb/s t.s. = 0.975
µs
9
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