Serial Interface with Time Slot Assigner
7-76
MC68360 USER’S MANUAL
MOTOROLA
Dynamic changes mean that the routing definition of a TDM can be modified while the
SCCs/SMCs are connected to the TDM. With fixed routing, a change to the routing requires
that all SCCs/SMCs connected to the TSA be disabled, the SI routing be modified, and then
all SCCs/SMCs connected to the TSA be reenabled before the new routing takes effect.
Dynamic changes divide portions of the SI RAM into current-route RAM and shadow RAM.
Once the current-route RAM is programmed, the TSA and SI channels can be enabled, and
TSA operation can begin. When the user decides that a change in routing is required, the
user programs the shadow RAM with the new route and sets the CSRx bit in the SI CR. As
a result, the SI will exchange the shadow RAM and the current-route RAM as soon as the
corresponding sync arrives and will reset the CSRx bit to signify that the operation is com-
plete. At this time, the user may change the routing again. Note that the original current-
route RAM is now the shadow RAM and vice versa. Figure 7-28 illustrates an example of
the shadow RAM exchange process.
If one TDM with dynamic changes is programmed, the initial current-route RAM addresses
in the SI RAM are as follows:
0–63 RXa Route
128–191TXa Route
and the shadow RAMs are at addresses:
64–127 RXa Route
192–255TXa Route
If two TDMs with dynamic changes are programmed, the initial current-route RAM address-
es in the SI RAM are as follows:
0–31 RXa Route
64–93 RXb Route
128–159TXa Route
192–223TXb Route
and the shadow RAMs are at addresses:
32–63 RXa Route
96–93 RXb Route
160–191TXa Route
224–255TXb Route
The user can read any RAM at any time, but for proper operation of the SI, the user must
not attempt to write the current-route RAM. The user can read the SI status register (SISTR)
to find which part of the RAM is the current-route RAM.
Beyond knowing which RAM is the current-route RAM, the user may wish to know which
entry that the TSA is currently using within the current-route RAM. This information is pro-
vided in the SI RAM pointer register (SIRP). The user may also externally connect one of
the four strobes to an interrupt pin to generate an interrupt on a particular SI RAM entry start-
ing or ending execution by the TSA.