MC68MH360EM33L Freescale Semiconductor, MC68MH360EM33L Datasheet - Page 305

• Manufacturer Part Number: MC68MH360EM33L
• Description: IC MPU QUICC ETHER 33MHZ 240FQFP
• Manufacturer: Freescale Semiconductor

Specifications of MC68MH360EM33L

• Processor Type: M683xx 32-Bit
• Speed: 33MHz
• Voltage: 5V
• Mounting Type: Surface Mount
• Package / Case: 240-FQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Features: -

the RAS signal of the DRAM bank. This RAS signal will remain active until another DRAM
bank is accessed. The page size is determined by the PGS bits in the GMR.
If a different bank of DRAM is accessed, followed by an access to a DRAM bank on which
page mode is selected, then the DRAM controller negates the RAS signal to the other bank
and asserts the particular RAS line for the page mode bank, followed by the rest of the
DRAM access. This is called a page mode normal cycle.
On each access to a DRAM bank in which the page mode is enabled and the previous
DRAM cycle was to that bank, the address of the last access to this bank is compared to the
current address. If the two addresses fall within the same page, then the access cycle
begins immediately with the assertion of the column address and CAS signal. This is called
a page hit.
In case of a page miss (the address of the last access and current address do not fall within
the same page), the RAS signal must be negated and held high for a period that matches
the value programmed in the WBTQ control field of the current DRAM region, and then a full
cycle (including row and column phases) is executed. This is the slowest DRAM access
since the RAS signal must first be negated, followed by the precharge time.
Since it is difficult to predict the performance impact of page mode, the user may wish to try
the application software with and without page mode enabled, and compare the results. The
ability to concentrate the code/data accesses into the same page of the DRAM is central to
achieving a performance improvement.
Some systems will need an additional wait state to perform write cycles during a page hit.
To gain a wait state, set the delay write cycle for the QUICC DWQ bit in the GMR of the
DRAM bank.
6.12.3 DRAM Burst Access Support
The DRAM controller supports burst accesses made by an external MC68EC040 (or other
MC68040 family member) if the BACK40 bit is set in the BR. The MC68EC040 requests a
burst to be performed with a line-fill indication on the SIZx pins (SIZ = 11) and the TTx pins.
In this case, the DRAM controller performs a normal access (RAS and CAS), followed by
requests to the DRAM for the next three sequential long-word operands (CAS only). The
DRAM controller automatically increments the addresses to the DRAM using the BADDR3–
BADDR2 pins.
The length of an MC68EC040 burst cycle can be distinguished from the length of the initial
access with the BCYC bits of the OR.
MOTOROLA
Page mode is supported only for the internal QUICC cycles or
external MC68030/QUICC cycles.
If any two DRAM banks overlap each other in their address
space, page mode must not be selected for either of those
banks.
Freescale Semiconductor, Inc.
For More Information On This Product,
MC68360 USER’S MANUAL
Go to: www.freescale.com
NOTES
System Integration Module (SIM60)
6-61