I2CWRITE/I2CREAD access hardware in the different way? (PCA9685 issues)

[CuriousOne]

Hello.
Trying to interact with PCA9685. No luck so far. Here's the code:

#config
CONFIG RETEN = OFF	
CONFIG INTOSCSEL = HIGH
CONFIG SOSCSEL = DIG
CONFIG XINST = OFF	    ;Enabled
CONFIG FOSC = INTIO1
CONFIG PLLCFG = OFF
CONFIG FCMEN = OFF	    ;Disabled
CONFIG PWRTEN = OFF	    ;Disabled
CONFIG BOREN = OFF	    ;Disabled in hardware, SBOREN disabled
CONFIG WDTEN = OFF	    ;WDT disabled in hardware; SWDTEN bit disabled
CONFIG CANMX = PORTB
CONFIG MCLRE = OFF


#endconfig


OSCTUNE.6 = 1 ; Enable 4x PLL
OSCCON = %01110000
ANCON1=0 'DISABLE ADC D3-D2-D1-D0-   b
ANCON0=%00000000                      'a
ADCON0=0
ADCON1=%11110000
TRISC=%00000000 'set PORTC as output all
TRISD=%00000000 'set PORTD as output all
TRISB=%00000000 'set PORTB as output all
TRISA=%00000000 'set PORTA as output all
TRISE=%00000000 'set PORTE as output all
define OSC 64


SCL_PIN VAR PORTC.0   ' I2C clock pin
SDA_PIN VAR PORTC.1   ' I2C data pin


PCA9685_CTRL_W CON $80   ' 8-bit write control byte
MODE1_REG      CON $00
MODE2_REG      CON $01
PRE_SCALE_REG  CON $FE
LED0_ON_L      CON $06


channel VAR BYTE          ' <-- define channel variable




' ----- Initialization -----
' Put device to sleep to set prescale
I2CWRITE SDA_PIN, SCL_PIN, PCA9685_CTRL_W, MODE1_REG, [$10]   ' SLEEP=1
PAUSE 5


' Set prescale for ~1 kHz PWM (example value)
I2CWRITE SDA_PIN, SCL_PIN, PCA9685_CTRL_W, PRE_SCALE_REG, [$06]


' Wake up, enable auto-increment
I2CWRITE SDA_PIN, SCL_PIN, PCA9685_CTRL_W, MODE1_REG, [$20]   ' AI=1, SLEEP=0
PAUSE 5


' Set outputs inverted + totem-pole
I2CWRITE SDA_PIN, SCL_PIN, PCA9685_CTRL_W, MODE2_REG, [$14]


' Force all channels full-off (outputs HIGH, LEDs off)
FOR channel = 0 TO 15
    I2CWRITE SDA_PIN, SCL_PIN, PCA9685_CTRL_W, (LED0_ON_L + channel*4), [$00,$00,$00,$10]
NEXT channel
PAUSE 10


' ----- Main loop -----
MainLoop:
    FOR channel = 2 TO 5
        ' Turn channel fully ON (use "full on": ON_H bit4 = 1)
        I2CWRITE SDA_PIN, SCL_PIN, PCA9685_CTRL_W, (LED0_ON_L + channel*4), [$00,$10,$00,$00]
        PAUSE 500


        ' Turn channel OFF again (full off: OFF_H bit4 = 1)
        I2CWRITE SDA_PIN, SCL_PIN, PCA9685_CTRL_W, (LED0_ON_L + channel*4), [$00,$00,$00,$10]
        PAUSE 200
    NEXT channel
GOTO MainLoop

I decided to check the signals with scope, and they're heavily distorted. (image 1) I have 10K pull-up resistors on both SDA and SCL pin. So to test the issues, I've added this simple code:

asda: 'small test for waveform shape
high SDA_PIN
pauseus 1
low SDA_PIN
pauseus 1
goto asda

When I run this code, the shape of the signal is perfect, as you can see from the 2nd image (and frequency is much higher, so definitely no capacitive loading issues). So what can be the reason I2CWRITE making so badly shaped signal?