C164CI_02 datasheet(73/484 Pages) INFINEON

73 / 484 page

C164CI/C164SI

Derivatives

Central Processing Unit (CPU)

User’s Manual

4-15

V3.1, 2002-02

System Clock Output Enable (CLKEN)

The system clock output function is enabled by setting bit CLKEN in register SYSCON

to ‘1’. If enabled, port pin P3.15 takes on its alternate function as CLKOUT output pin.

The clock output is a 50% duty cycle clock (except for direct drive operation where

CLKOUT reflects the clock input signal, and for slowdown operation where CLKOUT

mirrors the CPU clock signal) whose frequency equals the CPU operating frequency

(

fOUT = fCPU).

Note: The output driver of port pin P3.15 is switched on automatically when the CLKOUT

function is enabled. The port direction bit is disregarded.

After reset, the clock output function is disabled (CLKEN = ‘0’).

In emulation mode, the CLKOUT function is enabled automatically.

Segmentation Disable/Enable Control (SGTDIS)

Bit SGTDIS allows selection of either the segmented or non-segmented memory mode.

In non-segmented memory mode (SGTDIS = ‘1’), it is assumed that the code address

space is restricted to 64 KBytes (segment 0); thus, 16 bits are sufficient to represent all

code addresses. For implicit stack operations (CALL or RET), the CSP register is totally

ignored and only the IP is saved to and restored from the stack.

In segmented memory mode (SGTDIS = ‘0’) it is assumed that the entire address

space is available for instructions. For implicit stack operations (CALL or RET) the CSP

memory mode is selected.

Note: Bit SGTDIS controls whether the CSP register is pushed onto the system stack in

addition to the IP register before an interrupt service routine is entered, and it is

repopped when the interrupt service routine is left again.

System Stack Size (STKSZ)

This bitfield defines the size of the physical system stack located in the internal RAM of

the C164CI. An area of 32 … 512 words or all of the internal RAM may be dedicated to

the system stack. A so-called “circular stack” mechanism allows use of a bigger virtual

stack than this dedicated RAM area.

These techniques and the encoding of bitfield STKSZ are described in more detail in

Chapter 22.

C164CI Datasheet(PDF) 73 Page - Infineon Technologies AG