Cypress Semiconductor enCoRe CY7C64215 Uživatelský manuál stáhnout pdf (Strana 11)

August 17, 2011 Document No. 001-15340 Rev. *A

AN6073

Building a 1-ms Timer using Resources

on the CY7C64215

One common method is using an 8-bit PWM user module

and tweaking it to provide 1-ms interrupts. When there is a

constraint on resources, the user can configure the VC3

clock or the SOF interrupt sources to get 1-ms timer inter-

rupts. The three methods are explained below.

A. Configuring the 8-bit PWM in enCoRe III to behave as a 1-

ms interrupt timer.

The enCoRe III does not have a predefined 1-ms timer. How-

ever, one can be built from the 8-bit PWM user module avail-

able in enCoRe III. The steps for achieving this are given

below. A PSoC project that shows the basic configuration of

an 8-bit PWM as a 1-ms timer is attached with this project.

Note This project example was created solely for the purpose

of showing this conversion. The clock divider values may

change in your actual project and these should be accounted

for.

1. Start a PSoC Designer project with enCoRe III using ‘C’

for development.

2. Select the PWM user module and place it. (Select from

Device Editor - User Module Selection view and right click

in the Interconnect view to place it.)

3. In the Global Resources setting, choose VC1 = 16 and

VC2 = 6

4. In the User Module parameters section choose the

following:

– Clock = VC2 (This basically gives a clock of

24 MHz/96)

– Enable = high (to enable continuous count)

– Compare out = None

– Terminal Count = Row0 Output0 (To route the terminal

count signal to Port 0.0)

– Period = 255

– Interrupt type: Terminal Count (Terminal count hap-

pens every 256 periods of 24 MHz/96 clock =

1.024 ms)

– ClockSync: Sync to SysClk

– Invert Enable: Normal.

5. In the layout area, select Row0Output0 to

GlobalOutEven0.

6. In the Interconnect section select P0.0 to

GlobalOutEven0.

7. We are not concerned about Pulse Width and Compare

type since we are only looking to get 1-ms interrupt in this

example.

8. Hit the generate application button and go to the Applica-

tion Editor view.

9. In the main file, do the following:

– Enable Global interrupts

– Enable PWM interrupt

–Start PWM

10. In the PWM Interrupt ISR, custom code for 1-ms timer

interrupt can be included.

B. Configuring the VC3 clock divider to behave as a 1-ms

interrupt timer.

The VC3 clock can be used for 1-ms interrupt when there are

resource (digital blocks) constraints. Choosing the VC3 as

the 1-ms timer also gives greater flexibility to the system

clocks.

1. Select the appropriate VC3 clock source.

2. Choose a clock divider such that the output of VC3 gives

a 1-ms clock.

3. The interrupt is generated for every number of input clock

cycles = VC3 divider value+1

So if VC3 is sourced with a 1 KHz source and we choose the

divider value to be ‘0’, then interrupt occurs every cycle

(divider value+1 = 1) of the source i.e., every millisecond.

C. Using the USB SOF interrupt to behave as a 1-ms inter-

rupt timer.

The USB SOF interrupt occurs every 1 ms. Thus, the USB

SOF ISR can contain 1-ms ISR code. The USB SOF interrupt

only happens when there is USB traffic and may not be suit-

able in certain situations.

Summary

The CY7C64215 is functionally similar to the CY7C64x13

with integrated functionalities and configurable blocks. It has

a GUI based tool—PSoC Designer—that makes develop-

ment easy. This application note, with the PSoC TRM and the

enCoRe III data sheet will simplify the task of migrating

designs from CY7C64x13 to CY7C64215.

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