MPC8540 datasheet(529/1302 Pages) FREESCALE

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Memory Map/Register Definition

MPC8540 PowerQUICC III Integrated Host Processor Reference Manual, Rev. 1

Freescale Semiconductor

13-25

Table 13-14 describes LURT fields.

13.3.1.9

SDRAM Refresh Timer (LSRT)

The SDRAM refresh timer (LSRT), shown in Figure 13-12, generates a refresh request for all valid

banks that selected a SDRAM machine and are refresh-enabled (LSDMR[RFEN] = 1). Each time

the timer expires, all qualifying banks generate a bank staggering auto-refresh request using the

SDRAM machine.

Table 13-15 describes LSRT fields.

Table 13-14. LURT Field Descriptions

Bits

Name

Description

0–7

LURT UPM refresh timer period. Determines, along with the timer prescaler (MRTPR), the timer period

according to the following equation:

Example: For a 266-MHz system clock and a required service rate of 15.6 µs, given MRTPR[PTP] = 32,

the LURT value should be 128 decimal. 128/(266 MHz/32) = 15.4 µs, which is less than the required

service period of 15.6 µs.

Note that the reset value (0x00) sets the maximum period to 256 x MRTPR[PTP] system clock cycles.

8–31

—

Reserved

LSRT

Reset

0000_0000_0000_0000_0000_0000_0000_0000

Offset

0x0_50A4

Figure 13-12. LSRT SDRAM Refresh Timer (LSRT)

Table 13-15. LSRT Field Descriptions

Bits

Name

Description

0–7

LSRT

SDRAM refresh timer period. Determines, along with the timer prescaler (MRTPR), the timer period

according to the following equation:

Example: For a 266-MHz system clock and a required service rate of 15.6 µs, given PTP = 32, the

LSRT value should be 128 decimal. 128/(266 MHz/32) = 15.4 µs, which is less than the required

service period of 15.6 µs.

Note that the reset value, 0x00, sets the maximum period to 256

× MRTPR[PTP] system clock cycles.

8–31

—

Reserved

TimerPeriod

LURT

Fsystemclock

MRTPR PTP

[]

----------------------------------------

⎝⎠

⎛⎞

----------------------------------------------

TimerPeriod

LSRT

Fsystemclock

MRTPR PTP

[]

----------------------------------------

⎝⎠

⎛⎞

----------------------------------------------

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