ST9 datasheet(32/146 Pages) STMICROELECTRONICS

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ST9 USER GUIDE

Figure 14

. Stack Location Options

3.3 INSTRUCTION SET

The ST9 is said to be an 8/16-bit microcontroller. This means that although the size of the in-

ternal registers and the width of the data bus are 8 bits, the instruction set includes instructions

that handle a pair of registers or a pair of bytes in memory at once. These instructions repre-

sent roughly one half of the total instructions, which means that the ST9 can be programmed

with the same ease as if it were advertised as a full 16-bit device.

This is why it is well suited for C programming, as illustrated in this book.

Data Memory

(RAM)

Bottom

of Stack

Group E

System Registers

Group F

Paged Registers

R255

R240

R239

R00

Stack Pointer Low

Stack Pointer High

R255

R240

R239

R00

Bottom

of Stack

Group E

System Registers

Group F

Paged Registers

Stack Pointer Low

Stack Pointer High

Stack

System or User Stack

in Data Memory Space

System or User Stack

in Register Space

High byte of pointer irrelevant

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