MOTOROLA
Chapter 16. Memory Controller
16-31
Part IV. Hardware Interface
16.6.1 Requests
An internal or external masterÕs request for a memory access initiates one of the following
patterns:
¥
Read single-beat pattern (RSS)
¥
Read burst cycle pattern (RBS)
¥
Write single-beat pattern (WSS)
¥
Write burst cycle pattern (WBS)
These patterns are described in Section 16.6.1.1, ÒInternal/External Memory Access
Requests.Ó
A UPM periodic timer request pattern initiates a periodic timer pattern (PTS), as described
in Section 16.6.1.2, ÒUPM Periodic Timer Requests.Ó
An exception (reset or machine check (triggered by the assertion of TEA) occurring while
another UPM pattern is running initiates an exception condition pattern (EXS).
A special pattern in the RAM array is associated with each of these cycle type. Figure 16-32
shows the start addresses of these patterns in the UPM RAM, according to cycle type.
MCR-initiated
RUN
commands, however, can initiate patterns starting at any of the 64 UPM
RAM words.
Figure 16-32. RAM Array Indexing
16.6.1.1 Internal/External Memory Access Requests
When an internal master requests a new access to external memory, the address and type of
transfer are compared to each valid bank deÞned in BRx. The value in BRx[MS] selects the
UPM to handle the memory access. The user must ensure that the UPM is appropriately
initialized before a request.
Write Single-Beat Request
Read Burst Request
Read Single-Beat Request
Write Burst Request
RAM Array
Periodic Timer Request
Exception Condition Request
RSS
RBS
WSS
WBS
PTS
EXS
64 RAM
Words
Array Index
Generator
Содержание MPC860 PowerQUICC
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