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Do you get stuck doing PIC microcontroller timer calculation juggling between datasheet, calculator and your design requirements?

If so then you need some tools to automate the process.

Calculations

Typically

According to USFDA, a combination product is one composed of any combination of a drug and device; biological product and device; drug and biological product

you will need to focus on the end result which is usually to make the timer generate a frequency or measure a time period. This is fairly difficult when you first have to find the information in the datasheet and the

; or drug, device, and biological product and fixed dose combination would include two or more combinations of drug.

Examples of combination products may in

account for prescalers and postscalers etc.

PIC Timer 0 : Calculation example

Here is an example of the typical calculations for creating an 18ms interrupt repeat rate using PIC Timer 0.

Selecting a prescale

lude drug-coated devices, drugs packaged with delivery devices in medical kits, and drugs and devices packaged separately but intended to be used together.

r ratio of 1:128 gives the following interrupt period (with Fosc/4 or 4MHz/4 = 1MHz) and using the maximum overflow from Timer 0.

1/(1MHz/128/256) = 32.768ms

Obviously this is longer than you need but you can cut it

here is enormous increase in the number of combination products entering the market in the recent years. Combination products have proven advantages but fixe

down by changing the overflow point (in the interrupt). To do this you need the period of the frequency input to Timer 0 which is:

1/(1MHz/128) = 128us

This is the period of time for each count in Timer 0 i.e.

256

d dose combinations are still in the process of convincing regulatory authority on their advantages over the single ingredient formulations.

Combination pro

* 128us = 32.768ms

So by manipulating the overflow point you can set the overall interrupt period. The required period is 18ms so some calculations:

18ms/128us = 140.625 (nearest integer value is 141)

This is the n

ucts have become life saving products for the pharmaceutical companies who doesn’t have many innovative molecules in their product pipeline and have been inc

mber of counts required after which the interrupt is generated. To use it Timer 0 it is loaded in the following manner:

TMR0 = 256-143; // need 141 but Timer 0 looses 2 at load.

From this point on every 128us is cou

easingly used in the product life cycle management. Even the companies having product patents are trying to extend their product life cycle through the combi

nted by Timer 0 and it will overflow after 141 counts (or 18ms)

141 * 128us = 18ms

TCL Scripts for PIC Timer calculation

Every time you use any built in PIC timer you have to do these type of calculations and

nation products and maximize the revenues. But the companies involved in this practice are overlooking that they are burdening the patients both economically

the hardware in each timer is different and you'll also have to do battle with interrupts.

To make the process easy you can use three on-line (free) interactive script modules written in TCL (Tool Command Language). T

and physically. They need to rightly judge the benefits of the combination products and they have to even look at the risks involved when combining the produ

hey operate in a similar way to a Java applets.

Each of these scripts is geared towards the most typical use of each timer and lets you change prescaler, postscaler or register value using slider controls. This makes

ts. Some of the combination products were well accepted by physicians while others suffered. Companies involved in development of combination products are fi

it easy to experiment with different values as the result is immediately displayed in the web page (frequency and period are displayed from each part of the timer e.g. after the prescaler, after the register, after the

ding difficulty in defining their combination products and facing various challenges from selecting a combination to marketing it.

Following aspects would a

postscaler).

The above calculation is now trivial just move the sliders around until you get close to your desired PIC timer period and then adjust the timer value to home in on the correct answer.

So you can do wha

dd to the challenges in developing combination products:

Which markets to tap where the combination products can do fairly well?
Which combination prod

t-if type operations (all without a calculator in sight) e.g. 'I need a 15ms repeat rate'.

From Timer 2 the closest I could get is 15.136 (took 1 minutes to test) - perhaps I'll try timer 1 - Ah that gives an exact 15

cts are meaningful and rational?
Which therapeutic categories to select?
Which Combinations can address unmet needs of the patients?
Do combin

s (took 30 seconds to test). Just check with Timer 0 - this gives 15.040ms (took ~30 seconds to test).

Of course you can also set the main clock frequency (internal or external crystal) as well.

PIC Timer 0

T

tions increase the patient compliance?
What would be the developing cost?
How to tackle the risks encountered during combination product developmen

his has an 8 bit prescaler and an 8 bit timer and can be driven from an external clock.

Prescaler : 8 bit
Timer register : 8 bit

Link to t?

As combination products don't fit into the traditional categories of drugs, medical devices, or biological products, the USFDA is in the process of devel

er-0.html">PIC-Timer 0 calculator

PIC Timer 1

This has a 4 bit prescaler and an 16 bit timer and can be driven from an external clock. It can also be driven from a slow speed crystal e.g. 32kHz.

Prescaler

ping new procedures for reviewing their safety, efficacy and quality.

Professional from academic institutions, pharmaceutical industries, health care indust

: 4 bit Timer register: 16 bit

Link to PIC-Timer 1 calculator.

PIC Timer 2

This has a 4 bit prescaler and an 8 bit t

y and representatives from various regulatory agencies are working out to design the regulatory requirements for manufacture and sale of combination products

mer and an 8 bit period register and is only driven from the internal clock (Fosc/4)

Note: the Period register lets you create an output frequency with no further processing i.e. you don't have to update the timer reg

.

As there is an increasing trend of the combination products companies manufacturing such products should be able to tackle the problems involved in the de

ister value in an interrupt routine as you do with Timer 0 or Timer 1 - this makes it easy to use (although it's tricky to get right - unless you use the calculator scripts).

Prescaler : 2 bit (1:1, 1:4, 1:16)
Ti

elopment. They need to be wiser in analyzing the market trends and the regulatory requirements.

Companies that provide selfless information through particip

er register: 8 bit
Period register : 8 bit
Postscaler : 4 bit (1:1 to 1:16 inclusive)

Link to PIC-Timer 2 calculator.

tion in industry events and feedback to regulatory authorities would be able to face the challenges and will be successful in developing combination products

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