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PIC18F87J50 USART1 & 2 baud rate & I2C master (HW)

 
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PICoHolic



Joined: 04 Jan 2005
Posts: 224

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PIC18F87J50 USART1 & 2 baud rate & I2C master (HW)
PostPosted: Thu Apr 10, 2008 1:17 am     Reply with quote

Hey,

Code:

// Configuration Bits
#FUSES   NOWDT
#FUSES   PLL3
#FUSES   NOSTVREN
#FUSES   NOCPUDIV
#FUSES   H4_SW
#FUSES   NOXINST

// Clock configuration: 12MHz crystal
#use delay(clock=48000000)
#use rs232(baud=115200,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8, STREAM = SYN, UART1)
#use rs232(baud=38400,parity=N,xmit=PIN_G1,rcv=PIN_G2,bits=8, STREAM = CDR , UART2)
#use i2c(Master,Slow=100000,sda=PIN_C4,scl=PIN_C3, FORCE_SW)


Listing:
Code:

00D96:  MOVLW  08
00D98:  MOVWF  01
00D9A:  MOVLW  11
00D9C:  MOVWF  00
00D9E:  DECFSZ 00,F
00DA0:  BRA    0D9E
00DA2:  BCF    F8B.3
00DA4:  BCF    F94.3
00DA6:  MOVLW  11
00DA8:  MOVWF  00
00DAA:  DECFSZ 00,F
00DAC:  BRA    0DAA
00DAE:  MOVLB  1
00DB0:  RLCF   x41,F
00DB2:  BCF    F8B.4
00DB4:  BTFSC  FD8.0
00DB6:  BSF    F94.4
00DB8:  BTFSS  FD8.0
00DBA:  BCF    F94.4
00DBC:  BSF    F94.3
00DBE:  BTFSS  F82.3
00DC0:  BRA    0DBE
00DC2:  DECFSZ 01,F
00DC4:  BRA    0DC8
00DC6:  BRA    0DCC
00DC8:  MOVLB  0
00DCA:  BRA    0D9A
00DCC:  MOVLW  11
00DCE:  MOVWF  00
00DD0:  DECFSZ 00,F
00DD2:  BRA    0DD0
00DD4:  BCF    F8B.3
00DD6:  BCF    F94.3
00DD8:  NOP   
00DDA:  BSF    F94.4
00DDC:  MOVLW  11
00DDE:  MOVWF  00
00DE0:  DECFSZ 00,F
00DE2:  BRA    0DE0
00DE4:  MOVLW  11
00DE6:  MOVWF  00
00DE8:  DECFSZ 00,F
00DEA:  BRA    0DE8
00DEC:  BSF    F94.3
00DEE:  BTFSS  F82.3
00DF0:  BRA    0DEE
00DF2:  CLRF   01
00DF4:  MOVLW  11
00DF6:  MOVWF  00
00DF8:  DECFSZ 00,F
00DFA:  BRA    0DF8
00DFC:  BTFSC  F82.4
00DFE:  BSF    01.0
00E00:  BCF    F8B.3
00E02:  BCF    F94.3
00E04:  BCF    F8B.4
00E06:  BCF    F94.4
00E08:  MOVLB  0
00E0A:  RETLW  00
*


For USART1 the actual baud is greater than 115200 Shocked
I didnt test for UART2 yet.

Also HW I2C stalls, i had to do it by SW!

!?
Matro
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PostPosted: Thu Apr 10, 2008 1:42 am     Reply with quote

Quote:

For USART1 the actual baud is greater than 115200

What does it mean?
What is the difference?

You wrote #use delay(clock=48000000)
But is the HW UART driven by such a clock?

Check that the baudrate is correct according to the .lst file and the datasheet.

Matro.
PICoHolic



Joined: 04 Jan 2005
Posts: 224

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PostPosted: Thu Apr 10, 2008 2:01 am     Reply with quote

Quote:

What does it mean?
What is the difference?


PIC18F87J50 has 2 UARTs & 2 MSSPs
The actual Baud rate on UART1 is ~2.7 times faster than 115200.
The compiler should calculate the baud rate value according to the actual system clock which is 48MHz (12MHz internally).

I'm using a C compiler, why would i need to go to the listing and check for compiler bugs everytime!?!? Shocked
It's a real waste of TIME that i dont have much of it.

That's the main idea. So the purpose of my post is to find someone that has already done it instead of waisting time tracing the listing Confused

10x


Last edited by PICoHolic on Thu Apr 10, 2008 3:47 am; edited 1 time in total
Matro
Guest







PostPosted: Thu Apr 10, 2008 2:08 am     Reply with quote

I can't say more.
But just for test, if you replace #FUSES PLL3 by PLL1.
Is it now correct?

Matro.
PICoHolic



Joined: 04 Jan 2005
Posts: 224

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PostPosted: Thu Apr 10, 2008 3:46 am     Reply with quote

I cannot, since the PLL input needs a fixed 4MHz frequency i.e: PLL3 is a division by 3 --> 12/3 = 4MHz Wink

Also the CPU divider is set to 1 (no division) --> 48MHz system OSC --> 48/4=12MHz internal OSC

Thanks
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