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ST9 EXTERNAL MEMORY INTERFACE CONFIGURATION

5 SOFTWARE EXAMPLE

The code below shows a software example of a Large Memory Model interface (x150, x250

microcontrollers) with an external memory located in segment 24 of memory (and pointed to

by DPR3).

spp

#21

ld

R245, #082h

;EMR1 register: Normal mode & high-speed buffers

ld

R246, #050h;

;EMR2 register: zero wait states & (Bit 4)=1

spp

#0

ld

R252, #40h

; WCR: zero wait states

ld

R235, #20h

; MODER: No prescaler division & No High Impedance

spp

#3

ld

R250,#000h

;P6.5 in Alternate function

ld

R249,#0FFh

;

Push-Pull

ld

R248,#0FFh

;

(RW pin)

spp

#2

ld

R242,#000h

;Port 0 in Alternate function

ld

R241,#0FFh

;

Push-Pull

ld

R240,#0FFh

;

(Address LSB/Data multiplexed)

ld

R246,#000h

;Port 1 in Alternate function

ld

R245,#0FFh

;

Push-Pull

ld

R244,#0FFh

;

(Address MSB)

spp

#43

ld

R254,#000h

;Port 9 in Alternate function

ld

R253,#0FFh

;

Push-Pull

ld

R252,#0FFh

spp

#21

ld

R240, #0x00

;DPR0 register (Segment 0 for internal flash)

ld

R241, #0x01

;DPR1 register (Segment 0 for internal flash)

ld

R242, #0x80

;DPR2 register (Segment 20 for Internal RAM

ld

R243, #0x96

;DPR3 register (Segment 24 for External RAM)

sdm

; set data memory

ld

0xC000,#0xAA

;examples of data transfers

ld

0xC001,#0xAA

;

in external memory

ld

0xC002,#0xAA

;