ST9 datasheet(65/146 Pages) STMICROELECTRONICS

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ST9 USER GUIDE

4 USING THE ON-CHIP PERIPHERALS

This chapter introduces the main peripherals of the ST9 family. Each variant includes none,

one or several peripherals of each type. This allows you to select the variant that best fits your

requirements. For high-volume markets, you can order custom versions with exactly the type

and number of peripherals required, including the relatively exotic ones not described here but

available on request, such as videotext decoders etc.

4.1 PROGRAMMING THE CORE AND PERIPHERALS

In addition to describing how each peripheral works, we give examples of the code needed to

use them in several configurations. This code is available on the Companion software. You

can experiment with the original code or modify it to do the functions you require.

Configuring and using the core and the peripherals involves a considerable amount of bit ma-

nipulation in the registers. Many variables that drive microcontroller states are Boolean

values. To reduce the use of addressable space in registers, bits have been logically grouped

in bytes, so the majority of the control registers have their eight bits fully used.

To properly program these registers, you need to track the exact position of each bit in each

menting the source text so that it can be easily read and understood later. See the following

example:

R235,#11100000B ; R235 is register MODER

;

|||||||+-- HIMP : no foreign access to bus

;

||||||+--- BRQEN : no foreign access to bus

;

|||+++---- PRS2,1,0 : processor at full speed

;

||+------- DIV2 : crystal frequency divided by 2

;

|+-------- USP : user stack pointer in registers

;

+--------- SSP : system stack pointer in registers

spp

; SPI page

R254,#10000001B

;

|||||||+-- SPR0 : SPR1, SPR0 = 01: clock divided by 16

;

||||||+--- SPR1 :

;

|||||+---- CPHA : Input sampled on rising edge

;

||||+----- CPOL : Rest level of serial clock = 0

;

|||+------ BUSY : Set to ready

;

||+------- ARB : No I²C arbitration

;

|+-------- BMS : SPI used as a shift register (not I²C)

;

+--------- SPEN : SPI enabled

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