ST9 datasheet(22/146 Pages) STMICROELECTRONICS

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ST9 USER GUIDE

Figure 9

. Selecting Page Registers

As with the working registers, if a subroutine or an interrupt routine needs to access a periph-

eral that uses paged registers (which is very likely), you must save (or push) the register

pointer PPR at the beginning of the routine and restore it on exit.

Notes:

In both assembly and C languages, include files are supplied with symbolic names pre-defined

for all the peripherals. These names are unique for each peripheral; however several different

names relate to the same register, but in a different page. You must bear in mind that writing for

example (in C language):

S_ISR = 0;

/* clear serial peripheral error register */

does not automatically select the proper page; this statement must be preceded by another one

that selects the SCI page. Since no predefined C statement exists for this, a convenient way is

to define an assembler statement under the form of a macro that will read nicely in the C source.

An example of the correct way to access the SCI register is:

#define SelectPage(Page) asm ("spp %0":: "i" (Page)) ; /* pseudo function

to select a page */

SelectPage( SCI1_PG );

/* Select the serial peripheral page */

S_ISR = 0 ;

/* Clear serial peripheral error register */

3.1.7 Memory Management Unit

Like most microcontrollers, the ST9 has a bus for interfacing internal and external memories.

This allows you to store both programs and data. A special feature of the ST9 is that it can ad-

dress a 4 Mbyte single space to address ROM, RAM, EPROM, EEPROM, FLASH.

Group F

Paged Registers

Group E System Registers

R255

R240

R239

R224

R00

Groups 0 to D

Page Pointer Register (PPR)

R234

Page 3

PPR loaded using

instruction code spp #3.

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