PIC18 I2C maximum SCL clock freqency

Wei Deng · Guest

Hi, I want to use PIC18F452 (as master) with a MAX1238 (AD Converter as slave). The data sheet of MAX1238 says that it supports 400KHz Fast Mode and 1.7MHz High-Speed Mode. I checked the data sheet of PIC18F452, on page 151, it mentions that with the proper BRG value setting, PIC18F452 can generate 100kHz, 400kHz and 1MHz signal for the SCL clock. On Table 15-3 of page 151, from my understanding, it can even generate some non-standard SCL clock freqs, such as 312.5kHz, 308kHz, 333kHz. Have anyone tried successfully using MSSP module of PIC18F452 at a SCL frequency higher than 400kHz (i.e. 1MHz). I know that with CCS compiler, #use i2c (master, fast, ...) should work perfectly at 400kHz, but I really want to do more than that, even 1.7MHz (the max freq my slave supports).
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This message was ported from CCS's old forum
Original Post ID: 10119

Tomi · Guest

You can try to overwrite SSPADDR in early main() or just before you call i2c_start():

#byte SSPADD = 0xFC8

void main()
{
......... some initializations
SSPADD = 3; // or other value
......... rest of your code

OR:
void Access_My_i2c()
{
SSPADD = 3;
i2c_start();
i2c_write(0xA0);
..........
i2c_start(); // restart
i2c_read();
.........etc.
i2c_stop();
}

Check the bus speed by an O-scope.

:=Hi, I want to use PIC18F452 (as master) with a MAX1238 (AD Converter as slave). The data sheet of MAX1238 says that it supports 400KHz Fast Mode and 1.7MHz High-Speed Mode. I checked the data sheet of PIC18F452, on page 151, it mentions that with the proper BRG value setting, PIC18F452 can generate 100kHz, 400kHz and 1MHz signal for the SCL clock. On Table 15-3 of page 151, from my understanding, it can even generate some non-standard SCL clock freqs, such as 312.5kHz, 308kHz, 333kHz. Have anyone tried successfully using MSSP module of PIC18F452 at a SCL frequency higher than 400kHz (i.e. 1MHz). I know that with CCS compiler, #use i2c (master, fast, ...) should work perfectly at 400kHz, but I really want to do more than that, even 1.7MHz (the max freq my slave supports).
___________________________
This message was ported from CCS's old forum
Original Post ID: 10124