M E M m o d u l e c o n f i g u r a t i o n

Bits

Access

Mnemonic

Reset

Description

 

 

 

 

 

D18

R/W

A[26]

0

Enable A26 output

 

 

 

 

0 CS0WE_ is driven out the A26 pin

 

 

 

 

1 The A26 signal is driven out the A26

 

 

 

 

pin.

 

 

 

 

The bit settings determine how the NS7520

 

 

 

 

uses this signal. See "A27 and A26 bit

 

 

 

 

settings" on page 92 for more information.

 

 

 

 

 

D17

R/W

A25

1

Enable A25 output

 

 

 

 

Always set to 0; used for address bit 25.

 

 

 

 

 

D16

R/W

AMUX2

0

Internal/External/RAS/CAS mux

 

 

 

 

0 Normal operation

 

 

 

 

1 Drive the DRAM MUX control out

 

 

 

 

PORTA2, regardless of the AMUX and

 

 

 

 

DMUXS settings

 

 

 

 

Used to drive the DRAM RAS/CAS address

 

 

 

 

multiplexing control signal out the PORTA2

 

 

 

 

pin, regardless of the AMUX setting.

 

 

 

 

When set to 1, the memory controller drives

 

 

 

 

the DRAM RAS/CAS address multiplexing

 

 

 

 

control signal out the PORTA2 pin, for an

 

 

 

 

external address multiplexer to use for

 

 

 

 

DRAM RAS/CAS address multiplexing

 

 

 

 

control.

 

 

 

 

 

D15:00

N/A

Reserved

N/A

N/A

 

 

 

 

 

Table 36: MMCR bit definition

A27 and A26 bit settings

The A27 bit setting determines how the A27 signal is used by the NS7520. CS0OE_ is generated by an internal logical AND of the CS0_ and OE_ signals. The CS0OE_ signal goes active low when both CS0_ and OE_ are active low.

The A26 bit setting determines how the A26 signal is used by the NS7520. The CS0WE_ signal is generated by an internal logical AND of the CS0_ and WE_ signals. the CS0WE_ signal goes active low when both CS0_ and WE_ are active low.

When enabled, these signals maximize the read access timing for external memory peripherals attached to CS0. When using CS0OE_, the CS0 peripheral’s chip select input is attached to GND, and the read-access time for that peripheral is referenced

9 2

N S 7 5 2 0 H a r d w a r e R e f e r e n c e , R e v . D 0 3 / 2 0 0 6

Page 106
Image 106
Digi NS7520 manual A27 and A26 bit settings, Enable A26 output, Enable A25 output, AMUX2, Internal/External/RAS/CAS mux