C167CS datasheet(29/517 Pages) INFINEON

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C167CS

Derivatives

Architectural Overview

User’s Manual

2-12

V2.0, 2000-07

Peripheral Timing

Internal operation of CPU and peripherals is based on the CPU clock (

fCPU). The on-chip

oscillator derives the CPU clock from the crystal or from the external clock signal. The

clock signal which is gated to the peripherals is independent from the clock signal which

feeds the CPU. During Idle mode the CPU’s clock is stopped while the peripherals

continue their operation. Peripheral SFRs may be accessed by the CPU once per state.

When an SFR is written to by software in the same state where it is also to be modified

by the peripheral, the software write operation has priority. Further details on peripheral

timing are included in the specific sections about each peripheral.

Programming Hints

Access to SFRs

All SFRs reside in data page 3 of the memory space. The following addressing

mechanisms allow to access the SFRs:

• Indirect or direct addressing with 16-bit (mem) addresses must guarantee that the

used data page pointer (DPP0 … DPP3) selects data page 3.

• Accesses via the Peripheral Event Controller (PEC) use the SRCPx and DSTPx

pointers instead of the data page pointers.

• Short 8-bit (reg) addresses to the standard SFR area do not use the data page

pointers but directly access the registers within this 512 Byte area.

• Short 8-bit (reg) addresses to the extended ESFR area require switching to the

512 Byte extended SFR area. This is done via the EXTension instructions EXTR,

EXTP(R), EXTS(R).

Byte Write Operations to word wide SFRs via indirect or direct 16-bit (mem) addressing

or byte transfers via the PEC force zeros in the non-addressed byte. Byte write

operations via short 8-bit (reg) addressing can only access the low byte of an SFR and

force zeros in the high byte. It is therefore recommended, to use the bit field instructions

(BFLDL and BFLDH) to write to any number of bits in either byte of an SFR without

disturbing the non-addressed byte and the unselected bits.

Reserved Bits

Some of the bits which are contained in the C167CS’s SFRs are marked as ‘Reserved’.

User software should never write ‘1’s to reserved bits. These bits are currently not

implemented and may be used in future products to invoke new functions. In this case,

the active state for these functions will be ‘1’, and the inactive state will be ‘0’. Therefore

writing only ‘0’s to reserved locations provides portability of the current software to future

devices. After read accesses reserved bits should be ignored or masked out.

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