i2c bus tools - use your pc to send i2c messages and program eeproms

When you are evaluating the various I2C tools available on the market, it is important to look at the overall hardware/software packages rather than focusing on the I2C bus speed the device is capable of achieving. The two most popular I2C bus mastering tools use either the parallel port (LPT) or the serial port (COM).
The table, shown below, compares the parallel port and serial port I2C tools.

	I2Ctools.com (usb)	I2Ctools.com (parallel port)	RS-232 (COM port)
1. Actual Data Rate
2. I2C Bus speed
3. Software
4. Price
5. Simplicity
6. Multi-master Capability
7. Flexibility
8. Data Buffering
9. EEPROM Programming

Notes:
1. Data Rate: the actual data rate which can be transmitted by the parallel port solution can be two to three times the data rate of competing RS-232 solutions. This reason is quite simple: the RS-232 solution sends two hex characters for each data byte over the 115.2K RS-232 link to the micro before it can begin sending the data at over the I2C bus. A rough calculation shows that it would take over 180 ms to send 1K bytes using an RS-232 solution while the parallel port solution would take approximately 92ms to send the same data when transmitting at 100KHz. Raising the I2C frequency to 150KHz would lower the time required for this transmission to a little more than 61ms. The over-head of the RS-232 port is actually higher than the calculations indicate so you will get even lower data rates for the RS-232 solutions than we have estimated.

2. I2C Bus Speed: the i2c bus speed you can expect from the i2ctools parallel port solution is dependent upon the user's computer but you should expect speeds above 100KHz with today's computer systems. We typically see speeds over 150KHz on our computer systems but we cannot guarantee the value you will find on your system. The RS-232 solutions use a micro controller which are capable of achieving i2c bus speeds of 400 kHz, but as was noted above, the actual data rate is much lower.

3. Software: Our i2c tools include the capability to edit and program almost all i2c eeproms. They also include various screens enabling you to communicate to most i2c devices. The competition's packages include very basic software or require the user to utilize programs such as Hyper Terminal. When you are evaluating the various i2c products available on the market, please look at the software since this can be a more important factor than the hardware when measuring the productivity of a tool. We have spent a significant amount of time on our software and we are constantly upgrading it with new features as suggestions are received from our customers.

4. Price: LPT-to-I2C is obviously a very competitively priced package but if you look at LPT-to-I2C Professional, you will find the price difference even greater. We have seen packages costing $399 for products with capabilities similar to LPT-to-I2C Professional.

5. Simplicity: The hardware included with our parallel port products is powered directly from the parallel port so no additional power supply is required to use the product. Just plug it in and it's ready to use.

6. Multi-master Capability: RS-232 based products have micro controllers which give them multi-master capability (as long as the firmware supports it) while the parallel port products are generally single master capable devices.
Our usb products are multi-master capable.

7. Flexibility: the I2C bus frequency selection is limited in most of the RS-232 products on the market. Generally it will allow two frequencies: 100 kHz and 400 kHz. Our parallel port products allow you to select any frequency from 1KHz up to the maximum frequency allowed by the parallel port. Our usb-based products have the ability to transmit up to 1000KHz.

8. Data buffering: the I2C serial-based products cannot receive data as fast as it sends the data on the I2C bus. If the serial port is operating at 115.2K bit per second, then it actually receiving data at 56K bits per second (each byte is represented by two ASCII characters). Obviously, if you are sending data at 400K bits per second, the serial data is not going to keep up with the I2C data. While the I2C bus is waiting for the next data byte to be received from the serial bus, it must hold the clock line low to insert a wait state into the transmission. Many systems will time-out during this wait state. The parallel port systems are not totally immune to interruptions in the data transfer. The interruptions are not due to starving the data pipeline as is the case in the serial transfers. You will sometimes see interruptions in the parallel port transmissions due to Windows being a preemptive operating system.

9. EEPROM programming: the LPT-to-I2C and USB-to-I2C products include the ability to program most I2C-based EEPROMs in a target system. The software allows the user to select the address, page size, and write cycle time appropriate for the EEPROM. The data can be edited using standard hex characters or ASCII characters and then it can be saved in bin, hex, or mem formats. The software also verifies the data was correctly programmed after the EEPROM has been written.