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Chapter 9 SDRAM Controller

9-12

9.3.6

Bus Errors

The SDRAMC detects bus errors in the following situations:

•

Bus time-out occurs during Read or Write operation to the SDRAMC

•

ECC 2-bit fault error or Parity error occurs during SDRAM Read operation

If a bus error occurs when accessing the SDRAMC, then the SDRAMC will immediately assert the

current operation. Then, the current SDRAM cycle will end, remaining SDRAMC operations will be

aborted, a Pre-charge All command will be issued to SDRAM, then the SDRAMC will return to the Idle

state.

9.3.7

Memory Read and Memory Write

The RAS* signal, CAS* signal, WE*, signal, and ADDR[19:5] signal are set up 1 cycle before the

SDCS* signal is asserted in the case of the Read command, Write command, Pre-charge command, or

Mode Register Set command. The same set up time is observed even for active commands if the Active

Command Ready bit (SDCTR.DA) of the SDRAM Timing Register is set. Figure 9.5.1 is a timing

diagram of Single Read operation when the SDCTR.DA bit is cleared. Figure 9.5.2 is a timing diagram

of Single Read operation when the SDCTR.DA bit is set.

Burst or Single Read operation is terminated by the Pre-charge Active Bank command. Burst or

Single Write operation is terminated by the Auto Pre-charge Command.

9.3.8

Slow Write Burst

When the Slow Write Burst bit (SDCTR.SWB) of the SDRAM Timing Register is cleared, the data

changes at each cycle during Burst Write operation (Figure 9.5.6). When the Slow Write Burst bit is set,

the data will change every other cycle (Figure 9.5.7).

When the Slow Write Burst bit is set, all Write accesses will operate as tRCD = 3tCK regardless of the

setting of the RAS-CAS Delay bit (SDCTR.RCD) of the SDRAM Timing Register. The RAS-CAS

Delay bit setting becomes valid when Slow Write Burst access is invalid. The setting of the Slow Burst

bit does not have any effect on Read access.

9.3.9

Clock Feedback

When performing Read access at fast rates like 100 MHz, there may be insufficient set up time if an

attempt to directly latch Read data with the internal clock is made. With the TX4937, it is possible to

latch data using SDRAM clock SDCLKIN that is input from outside the chip. Please connect

SDCLKIN to one of the SDCLK[3:0] pins and the external source.

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