Requests; Internal/External Memory Access Requests - Freescale Semiconductor MPC850 User Manual

User-Programmable Machines (UPMs)

15.6.1 Requests

An internal or external master's 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 15.6.1.1, "Internal/External Memory Access
Requests."
A UPM periodic timer request pattern initiates a periodic timer pattern (PTS), as described
in Section 15.6.1.2, "UPM Periodic Timer Requests."
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 types. Figure
15-32 shows the start addresses of these patterns in the UPM RAM, according to cycle type.
MCR-initiated commands, however, can initiate patterns starting at any of the 64 UPM
RUN
RAM words.
Read Single-Beat Request
Read Burst Request
Write Single-Beat Request
Write Burst Request
Periodic Timer Request
Exception Condition Request

15.6.1.1 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 defined 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.
Array Index
Generator
Figure 15-32. RAM Array Indexing
MPC850 Family User's Manual
RAM Array
RSS 0x00
RBS 0x08
WSS 0x18
WBS 0x20
PTS 0x30
EXS 0x3C
64 RAM
Words