Contained within this html page are scripts that will work in conjunction with the VB4221. The BV4221 is a USB to I2C converter so that by connecting the BV4221 to the PC and also to one or more I2C devices, it is possible to control them from this browser document.

There are several documents in the series all of which concentrate on one particular I2C device, the first green and second blue forms are for communicating with the BV4221 and any form or text that follows is for the particular device in question. This text uses BV scripts and so depending on how the browser is configured there may be security warnings. Feel free to view the scripts and use as you like in your own applications.

Because VBScript is used then an IE (Microsoft) compatible browser is required. VBscript can also be made to run stand alone and within Microsoft applications such as Excel and Word. The script in this file should run with little modification.

There is a timer that can be driven from an external source or the internal 2MHz oscillator. The value of the timer register can be read from the I2C bus or the output can be fed to an external pin. The external pin will toggle at each overflow of the register.

The timer is working all of the time but by default it is set to get it’s input from pin 17 so reading the timer value with command 13 will not reveal any changes unless there is some change on pin 17 which is set to input at reset.

The timer consists of an 8 bit register and an 8 bit presaler. The values of the prescaler can be set to the following:

Note that value 8 will turn off the prescaler and allow the clock source to go straight to the timer counter.

The timer value can be loaded with any value from 0 to 230. This value is loaded into the counter which then increments until it overflows at value 255. At this point, if set the output at pin 6 will toggle and the value will be loaded into the timer again.

The result of this is that a value of 0 will give the largest delay (lowest frequency) and 230 will give the highest delay.

This table gives some examples of the output at pin 6 when the internal clock is used. The period is one full cycle, i.e. pin 6 goes from low to high and then back to low.

See the scope output: this is for the lowest frequency when the prescaler is set at 7 and the timer is set to 0. The period shown in Figure 2 is 65mS.

Command 13 will automatically set pin 6 (i/o 3) to be an output and using command 2 to set it either high or low will make no difference.