Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 474

Memory Controller
15.6.1.2 UPM Periodic Timer Requests
Each UPM contains a periodic timer that can be programmed to generate periodic service requests of a
particular pattern in the RAM array.
timer request generation. In general, the periodic timer is used for refresh cycle operation. MxMR[PTx]
defines the period for the timers associated with UPMx. If MxMR[PTxE] is set, the periodic timer of UPMx
requests a transaction when the timer period expires.
System Clock
Figure 15-33. Memory Periodic Timer Request Block Diagram
15.6.1.3 Software Requests—MCR
Software can start a request to the UPM by issuing a
have their own signal handshaking protocol to put them into special modes, such as self-refresh mode.
Other memory devices must be issued special commands 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, and the MCR
at the specified RAM location until it encounters a RAM word with its LAST bit set.
15.6.1.4 Exception Requests
When the MPC885 under UPM control initiates an access to a memory device, the external device may
assert TEA, SRESET, or HRESET. 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
which defines how the UPM deasserts its signals in a controlled manner.
15.6.2 Programming the UPM
The UPM is a microsequencer that requires microinstructions or RAM words to generate signal timings
for different memory cycles. Program the UPMs in the following steps:
1. Write patterns into the RAM array.
2. Program MPTPR.
3. Program the machine mode register (MAMR and MBMR).
4. Set up BRx and ORx.
15-34
Figure 15-33 shows the hardware associated with memory periodic
BRG
Prescaler and
Memory
External Bus
Periodic
Clock
Timer
Divider
Prescaler
(In SCCR)
(In MPTPR)
RUN
command is used to run the cycle. The UPM runs the pattern beginning
RUN
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Periodic
Timer A
(PTA)
Periodic
Timer B
(PTB)
Command
command to the MCR. Some memory devices
RUN
UPMA Periodic
Timer Request
UPMB Periodic
Timer Request
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