C167CS-4RM datasheet(65/517 Pages) INFINEON

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C167CS

Derivatives

The Central Processing Unit (CPU)

User’s Manual

4-15

V2.0, 2000-07

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.

While signal CLKOUT is tightly coupled to the CPU clock signal, the programmable

frequency signal FOUT (controlled by register FOCON) may be output on this pin.

Please refer to Chapter 21.

Segmentation Disable/Enable Control (SGTDIS)

Bit SGTDIS allows to select 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) and 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 whole address

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

memory mode is selected.

Note: Bit SGTDIS controls if 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, which is located in the internal

RAM of the C167CS. 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 to use a

bigger virtual stack than this dedicated RAM area.

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

in Chapter 22.

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