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I have several Microchip 8K EEPROMs on my Cypress FX2LP's I2C bus. To read from these larger ROM chips, a specific I2C protocol must be followed...
* Start token Write 2-byte mem location to I2C address * Start token Read n data bytes from I2C address * Stop token
Unfortunately, using the default EXUSB.lib functions results in a "Stop" token placed on the bus after the EZUSB_WriteI2C() function is called...
* Start token Write 2-byte mem read-location to I2C address 0xA6 * Stop token * Start token Read data from I2C address 0xA6 * Stop token
Looking at the EZUSB.lib source code, most of the work is done by an ISR called "i2c_isr()". Obviously, I must modify this function to omit the "Stop" token under certain conditions while writing to the I2C bus.
The problem is, I can't seem to remap the I2C interrupt vector to my new function. I've rebuilt the EZUSB library without the I2C related functions. But when I build my project, a warning message claims my "new_i2c_isr()" function is unused and will be omitted from the image. In other words, the Keil "interrupt" language extension doesn't seem to work in my code...
void new_i2c_isr (void) interrupt 9 { // new code here }
So how do I map my new_i2c_isr() function to the I2C interrupt vector? Has anyone ever modified the I2C behavior of the EZUSB lib?
It's working now. Here's what happened...
#1) The wrong chip was soldered on the board initially so that a 16-byte write buffer was needed. I kept getting weird buffer wrap-around errors when writing.
#2) After putting on the correct 24AA64, the 32-byte buffer still didn't work.
#3) Everything worked as expected once I switched back to the default EXUSB_WriteI2C() function when setting the memory read location.
I was initially led off-trail by the 24AA64 docs. The "Stop" token IS REQUIRED when setting the memory read location. The internal address pointer does not update correctly unless the write is framed with the "Stop" token.
Thanks for the help Tsuneo!
As you seem to conclude this I2C EEPROM problem, this comment may be unnecessary,
"The "Stop" token IS REQUIRED when setting the memory read location."
The repeated START (without STOP) also works. But you need an another state variable (flag) to control the flow in the I2C ISR. It takes fare amount of changes from the source code of the Cypress I2C library.
Both methods work. Then, choose one, good for you :-)
Tsuneo