Motorola PowerQUICC II MPC8280 Series Reference Manual page 470

Register Descriptions
Table 11-14 describes LURT fields.
Table 11-14. Local Bus-Assigned UPM Refresh Timer (LURT)
Bits Name
0–7 LURT Refresh timer period. Determines the timer period according to the following equation:
This timer generates a refresh request for all valid banks that selected a UPM machine assigned to
the local bus (MxMR[BSEL] =1) and is refresh-enabled (MxMR[RFEN] =1). Each time the timer
expires, a qualified bank generates a refresh request using the selected UPM. The qualified banks
are rotating their requests.
Example: For a 25-MHz system clock and a required service rate of 15.6 µs, given
MPTPR[PTP] = 31, the LURT value should be 11 decimal. (12*32)/25 MHz = 15.36 µs, which is less
than the required service period of 15.6 µs.
11.3.10 60x Bus-Assigned SDRAM Refresh Timer (PSRT)
The 60x bus assigned SDRAM refresh timer register (PSRT) is shown in Figure 11-16.
0
Field
Reset
R/W
Addr
Figure 11-16. 60x Bus-Assigned SDRAM Refresh Timer (PSRT)
Table 11-15 describes PSRT fields.
Table 11-15. 60x Bus-Assigned SDRAM Refresh Timer (PSRT)
Bits Name
0–7 PSRT Refresh timer period. Determines the timer period according to the following equation:
This timer generates refresh requests for all valid banks that selected a SDRAM machine assigned
to the 60x bus and is refresh-enabled (PSDMR[RFEN] = 1). Each time the timer expires, all banks
that qualify generate a bank staggering auto refresh request using the SDRAM machine. See
Section 11.4.10, "SDRAM Refresh."
Example: For a 25-MHz system clock and a required service rate of 15.6 µs, given
MPTPR[PTP] = 31, the PSRT value should be 11decimal. (12*32)/25 MHz = 15.36 µs, which is less
than the required service period of 15.6 µs.
11-32
Freescale Semiconductor, Inc.
TimerPeriod =
TimerPeriod =
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Description
( ) × ( [
⎛
LURT + 1 MPTPR PTP
----------------------------------------------------------------------------------------
⎝
Bus Frequency
PSRT
0000_0000
R/W
0x1019C
Description
( ) × ( [
⎛
PSRT + 1 MPTPR PTP
-------------------------------------------------------------------------------------- -
⎝
Bus Frequency
] )
⎞
+ 1
⎠
7
] )
⎞
+ 1
⎠
MOTOROLA