Z8FS040 datasheet(51/56 Pages) ZILOG

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ZMOTION

TM Detection and Control Family

Product Specification

PS028506-1110

PRELIMINARY

Appendix B

PIR Engine Initialization and Control

Description

The application software must execute an initialization procedure to enable the PIR engine. Once the

PIR engine is enabled, it runs in the background from the ADC interrupt. Every ADC conversion

generates an interrupt and the PIR engine performs its functions during this time. The user application

code runs in the foreground and monitors the status through the API and performs any other functions

required for the application.

The PIR engine also requires a one-second tick to perform several house-keeping operations and to

keep track of its sampling rate. This needs to be provided by the user application through

Status/Control Register 1 (Engine Timer Tick). This bit should be set to a 1-once per second by the

application software to provide the engine with a 1-second time base. The accuracy of this time is not

critical, but should be within +/- 10%.

There are two basic modes in which the PIR engine operates: Normal Scan Rate mode and Low Scan

Rate mode. See description of the PIR Scan Rate bit in the PIR Status/Control Register 1 for more

details.

The PIR engine runs in the background from the ADC interrupt (initiated by the application). Engine

processing is done during the ADC interrupt. Therefore CPU loading is based on the sample rate of

the ADC. To ensure a consistent sample rate the Engine needs to know the MCU operating frequency

(System Clock Frequency). It uses the Flash Frequency Control Registers to determine the operating

frequency which must be initialized prior to starting the Engine.

The Flash Frequency High (FFREQH) and Flash Frequency Low Byte (FFREQL) registers combine to

form a 16-bit value FFREQ primarily to control timing for Flash program and erase functions. This

value is also used by the PIR software engine to calculate the required sample rate of the ADC and

other functions. The 16-bit value for FFREQ is the System Clock Frequency in KHz and is calculated

using the following equation.

FFREQ[15:0] = {FFREQH[7:0],FFREQL[7:0]} = (System Clock Frequency)/1000

Basic steps for initializing the PIR engine – this process is common to both Normal Scan Rate and

Low Scan Rate modes:

1. Set up API control registers (standard and advanced)

2. Initialize FFREQH and FFREQL registers with MCU clock frequency

3. Write PIR Enable Pattern to PIR Enable Register

4. Call PIR Init

5. Initialize any Application specific I/O and peripherals

6. Enable interrupts

7. Ensure PIR Sensor Stable bit (ePIR_SC0:0) is set

8. Continue with application

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