CCS C Compiler Manual PCB / PCM / PCH

Common Questions & Answers
How does the PIC® connect to an I2C device?
Two I/O lines are required for I2C. Both lines must have pullup registers. Often the I2C device
will have a H/W selectable address. The address set must match the address in S/W. The
example programs all assume the selectable address lines are grounded.
How much time do math operations take?
Unsigned 8 bit operations are quite fast and floating point is very slow. If possible consider fixed
point instead of floating point. For example instead of "float cost_in_dollars;" do "long
cost_in_cents;". For trig formulas consider a lookup table instead of real time calculations (see
EX_SINE.C for an example). The following are some rough times on a 14-bit PIC®. Note times
will vary depending on memory banks used.
20 mhz PIC16
int8 [us]
int16 [us]
int32
[us]
float
[us]
+ 0.6 1.4 3 111.
- 0.6 1.4 3 113.
* 11.1 47.2 132 178.
/ 23.2 70.8 239.2 330.
exp() * * * 1697.3
ln() * * * 2017.7
sin() * * * 2184.5
40 mhz PIC18
int8 [us] int16 [us] int32 [us] float [us]
361