OpenServo.com

youthreewire · Joined: 30 Nov 2008 Posts: 39

As I understand the following command changes the position:
registers_write_word(REG_SEEK_HI, REG_SEEK_LO, 0x0100);

0x0100 is the position value.But there are always two registers REG_SEEK_HI and REG_SEEK_LO associated with the position.Why are two registers required?

Also REG_MIN_SEEK_LO,REG_MIN_SEEK_HI and REG_MAX_SEEK_LO ,REG_MAX_SEEK_HI are for providing limitation to the servo to save from mechanical flaw which can result from overturning.

ginge · Posted: Wed Dec 17, 2008 1:33 pm Post subject:

Hi,

Each register is an 8 bit value, and can only hold values between 0 to 255

The HI and LO values are used to allow a value greater than 255 to be stored, by storing as a 16bit variable. THis allows values between the range of 0 - 65535

The OpenServo does some simple bit shifting to combine the HI and LO values of the 2 8 bit registers into 1 16 bit value.

The easiest way to explain is by example:

255 in binary is:
11111111

65535 in binary is:
HI LO
11111111 11111111

SO....

New position to be set: 0x0100 in decimal this is 256, or one too large for a single 8 bit register.

So if we show this in binary form...

HI Bit LO bit
00000001 00000000

so when we write the position to the servo, we send 2x 8 bit bytes. The first (HI) is 0x01 the LO is 0x00

So as you can se it is the same as 0x0100

I would highly recommend learning how bits bytes, and bitwise work. You will need this to learn how to manipulate large variables in a small micro

I googled and found this great looking resource.
http://www.cprogramming.com/tutorial/bitwise_operators.html

Barry
_________________
http://www.headfuzz.co.uk/
http://www.robotfuzz.co.uk/

youthreewire · Joined: 30 Nov 2008 Posts: 39

mpthompson · Joined: 02 Jan 2006 Posts: 650 Location: San Carlos, CA

ginge · Posted: Wed Dec 17, 2008 11:04 pm Post subject:

ginge · Posted: Wed Dec 17, 2008 11:48 pm Post subject:

youthreewire · Joined: 30 Nov 2008 Posts: 39

Coming back alive after a long time.(Sorry for keeping the thread inactive for some time,was involved in other work).Once again I thank Ginge and Mike for their valuable time.

I think TWI.c and eeprom.h go together.The TWI commands write the register values buy updating the higher 4 bits and the lower 4 bits and are stored in the eeprom.

ginge · Posted: Sat Jan 31, 2009 9:24 pm Post subject:

Welcome back Youth!

"I think TWI.c and eeprom.h go together.The TWI commands write the register values buy updating the higher 4 bits and the lower 4 bits and are stored in the eeprom."

Um, this isn't really how OpenServo communication works.

TWI.c has routines to read the values from the hardware TWI module, and then fills a global data array called registers with the data at the relevant position. The eeprom doesn't come into the communication method at all. The eeprom stores the TWI module's slave address and other configuration variables.
It doesn't make sense to use the eeprom in that way, and would wear out the storage cells pretty quickly.

I can show you how the code paths work within twi.c if you want.

Baz
_________________
http://www.headfuzz.co.uk/
http://www.robotfuzz.co.uk/

youthreewire · Joined: 30 Nov 2008 Posts: 39

sikolymester · Joined: 19 Mar 2010 Posts: 1

Hi, I made a PCB following the v2.1 schematic.
Now I would like to use an atmega8 on it, because it is less costly than an atmega 168. The problem is, that I can't get any code to work in it.
Can you help me finding the files I have to use in the CVS repository.

I can get the code to compile, but realy nothing happens. Only thing that seems to work is reading out the position with the openservo.

Help would be appreciated. Thanks!