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Microcontroller
Peripheral Timing
Calculator

Philips 8xC552, 8xC554, 8xC591 - I2C baud rates

Enter your external clock rate, the desired baud rate and then click on the "Calculate" button.

 

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The I2C Bus

The 8051 Microcontroller

Clock frequency (in MHz): (mhz)
Desired baud rate (in bps): (bps)

Fixed Baud Rates

The I2C baud rate is set with the bits CR2..CR0 in Special Function Register S1CON. Depending on their contents, the following baud rates can be achieved:

Bits CR2..CR0

 Baud rates
0
mhz/256
1
mhz/224
2
mhz/192
3
mhz/160
4
mhz/960
5
mhz/120
6
mhz/60
7 Using Timer 1 to
generate vriable
baud rate

Variable Baud Rate

If bits CR2..CR0 are set all set, Timer 1 can be used to generate a variable baud rate. Timer 1 needs to be configured to run in Mode 2. The counter reload value to achieve the desired baud rate is calculated below:

  Values
Desired Timer 1 run time
rate=mhz/(96*bps)
Closest possible
Timer 1 reload value
rel=256-rate
Real baud rate achieved
bpsr=mhz/(96*(256-rel))
Difference to the desired
baud rate
var=(bpsr-bps)/bps
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Author: Olaf Pfeiffer

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