M e m o r y C o n t r o l l e r M o d u l e

The NS7520 provides the A10/AP multiplexing function using the CAS0_ pin. During the active command, the CAS0_ pin is driven with the logical value of one of the address bits A[21:18] as a function of the port size configuration defined in Chip Select Option Register A and the mux mode defined in the Chip Select Base Address register.

This table defines which address bit is driven in each situation:

Mux mode

x32

x16

x8

 

 

 

 

0

20

19

18

 

 

 

 

1

21

20

19

 

 

 

 

During the read or write commands, the NS7520 drives a 0 on the CAS0_ pin (indicating that automatic precharge should not be performed). During the precharge command, the NS7520 drives a 1 on the CAS0_ pin (indicating that all banks should be precharged.)

Command definitions

SDRAMs operate according to a series of command codes that are issued while chip select input is active low. The command codes are registered using the low-to-high transition of the synchronous clock. NS7520 implementation requires that all SDRAMs are synchronized to the NS7520 BCLK signal.

Command

CSx_

A13:0

CAS3_ RAS#

CAS2_ CAS#

CAS1_ WE#

CAS0_ A10/AP

 

 

 

 

 

 

 

Inhibit

1

X

X

X

X

X

 

 

 

 

 

 

 

NOP

0

X

1

1

1

X

 

 

 

 

 

 

 

Active

0

Bank/row

0

1

1

A10

 

 

 

 

 

 

 

Read

0

Column

1

0

1

0

 

 

 

 

 

 

 

Write

0

Column

1

0

0

0

 

 

 

 

 

 

 

Burst Term

0

X

1

1

0

X

 

 

 

 

 

 

 

Precharge

0

X

1

1

0

X

 

 

 

 

 

 

 

Refresh

0

X

0

0

1

X

Table 45: SDRAM command definitions

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Digi NS7520 manual Command definitions, Sdram command definitions, Mux mode X32 X16, Nop