Motorola MPC8260 - Manual (Page 342)

10-66 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA
Part III. The Hardware Interface
All local bus refreshes are done using the refresh pattern of UPMB. This means that if
refresh is required on the local bus, UPMB must be assigned to the local bus and
MBMR[RFEN] must be set. It also means that only one refresh routine should be
programmed for the local bus, and be placed in UPMB, which serves as the local bus refresh
executor. If refresh is not required on the local bus, UPMB can be assigned to any bus.
UPMC can be assigned to any bus; there is no need to program its refresh routine because
it will use the one in UPMA or UPMB, according to the bus to which it is assigned.
Figure 10-57. Memory Refresh Timer Request Block Diagram
10.6.1.3 Software RequestsÑ RUN Command
Software can start a request to the UPM by issuing a RUN command to the UPM. Some
memory devices have their own signal handshaking protocol to put them into special
modes, such as self-refresh mode. Other memory devices require special commands to be
issued on their control signals, such as for SDRAM initialization.
For these special cycles, the user creates a special RAM pattern that can be stored in any
unused areas in the UPM RAM. Then the
RUN command is used to run the cycle. The UPM
runs the pattern beginning at the speciÞed RAM location until it encounters a RAM word
with its LAST bit set. The
RUN command is issued by setting MxMR[OP] = 11 and
accessing the UPMx memory region with a single-byte transaction.
Note that the pattern must contain exactly one assertion of PSDVAL (UTA bit in the RAM
word, described in Table 10-35), otherwise bus timeout may occur.
10.6.1.4 Exception Requests
When the MPC8260 under UPM control initiates an access to a memory device, the
external device may assert TEA or SRESET. The UPM provides a mechanism by which
memory control signals can meet the timing requirements of the device without losing data.
The mechanism is the exception pattern that deÞnes how the UPM deasserts its signals in
a controlled manner.
10.6.2 Programming the UPMs
The UPM is a microsequencer that requires microinstructions or RAM words to generate
signal timings for different memory cycles. Follow these steps to program the UPMs:
1. Set up BRx and ORx.
2. Write patterns into the RAM array.
60x bus assigned UPM
Local bus assigned UPM
System Divide by PURT PTP Prescaling
Divide by LURT
refresh timer request
refresh timer request
Clock