Hi All

I have been working on a project for some time but due to time constraints have not had time to pursue for some months

My project involves sending data too and from a Master / Slave using two PICS

But for the time being I found a nice write up on the web to send a piece of data to an EPROM, read it back and then light 8 LEDS on the PIC

The code uses a PIC16F877 (which I have not currently got)

I do have several 16F887's with internal clock

So I decided to modify the code to fit

When I compiled it, it did not like the #Define statements

Much research on the web did not enlighten me (It looks like C language or a macro)

So I cheated and used CBLOCK to define the labels then moved the values into the labels using
movlw 0x34
movlf DATA
where before they used #Define DATA
#define LC01DATA H’34’ ; Sample data to write to EEPROM

I cut out the baud rate part of the program because the compiler did not like it, and it all passes

So now I need to put the clock speed back in and simulate the program

Did the same trick with cblock but the compiler complained

I think that I was trying to put 4,000,000 into memory of 8 BITS
This is 3D0900 in Hex

I guess with CBLOCK I have sequentially used memory in blocks of 8 BITS

So the maximum value is FF per memory address

The D'100' should work as Binary 64

The formula seems to be FOSC divided by 4* (SSPADD +1)

Basically resulting in 100 MHZ Clock Rate for a 4MHZ Oscillator

Is there a simpler way to program this statement in (using assembler)

Can someone explain the #DEFINE and why MPLABSIM will not compile it

I am confused about this statement
BANKSEL SSPADD
movlw (FOSC / (4 * BAUD)) - 1 ; Calculates SSPADD
movwf SSPADD ; for desired Baud rate
; and sets up SSPADD

Can they not say
In effect 4,000,000 / (400))
= 100,000
minus 1

So SSPADD = 99999
11000011010011111 in binary

Which is surely too large for the SSPADD register ??

Confused ?

I know I am



Any help appreciated





For info I found the tutorial program here

It is a copy of the original Microchip document

http://galaxy.eti.pg.gda.pl/katedry/ksg/dydaktyka/dla_studentow/i2c.pdf

 

You need to distinguish between arithmetic done by the compiler at compile time on a desktop PC, and arithmetic done at runtime on the PIC processor itself. Although #define is a construct from the C language, many assemblers have adopted the syntax and semantics for TEXT SUBSTITUTION MACROS. A text substitution macro operates in a pass over the source code BEFORE any actual compilation or assembly happens. Once the source code has been pre-processed it is passed to the assembly or compilation phase with ALL symbolic constants replaced by their equivalent numeric strings. Sting substitution has no knowledge of word sizes or processor word length. It is completely independent. You need to start over again with the original source code, understand the operation of text substitution macros, and adapt the code to your environment. What you have now is probably too hacked up to recover.

BTW -- Nobody would run I2C at 100 baud. 100k to 400k would be typical. In this hardware 100 baud would be un-realizable as you have already observed

 

Ok thanks for the input. I keep coming across the #Define syntax in a lot of code. I will have to try and find a good tutorial.

I use the MPLAB asm compiler

As this code originated from a Microchip tutorial, I thought it would just compile straight away without modification. I must admit I did not try it using the PIC16F877 which should just compile

I am aiming for 100khz baud rate (standard I2C)

There is lots of info about baud rate and I2C I just need to find a post with all the info in one place.

AN735 has some useful info although based on another PIC

There are a few things unclear

Do I use OSCON register to setup the clock or is this not required for I2C ?

I assumed I would need to specify XT as in the Microchip example the configure shows XT

However this is based on a chip with external clock vs one with internal

I was going to go with
BIT 0= Internal Oscillator used for system clock (SET TO 1)
BIT 1=LTS LFINTOSC is not stable (SET TO 0) as not using low freq ??
BIT 2=HTS HFINTOSC is stable (SET TO 1) as using 100khz ??
BIT 3=OSTS Device is running from Internal Oscilator (SET To 0)
BIT 4-6=IRCF 4 MHZ (SET TO 110)
BIT 7 not used (SET TO 0)

Equally I could be completely wrong

The equation for BIT rate appears to be (from AN75)

;Bit rate calc
SSPADD=( (FOSC/BIT RATE)/4) -1

;Bit rate setup
Movlw b'00001001'
Banksel SSPADD
movwf; baud rate =400 kHz@ 16MHZ

It then sets the slew rate, but I would need to set this different to the application note as using a lower speed

So for this example FOSC = 16MHZ (clock speed)
BIT RATE = 400khz ( desired baud rate)
(16,000,000 / 400,000) = 40
40/4= 10
10 -1 =9
Therefore SSPADD = 9
Hence movlw b'00001001' as this = decimal 9

So in my case

FOSC=4 MHZ (clock speed)
BIT RATE = 100khz

(4,000,000 / 100,000) = 40
40/4= 10
10-1=9
Therefore SSPADD =9

If I was to increase my clock to 8MHZ
FOSC=8MHZ
BIT RATE = 100 KHz
(8,000,000 / 100,000)=80
80/4 = 20
20 - 1 = 19
Therefore SSPADD = 19

Movlw b'001001111'
Movwf SSPADD

So hopefully this is the gist of the baud rate, I just need to now work out the config declaration ( as in the case of the PIC16F887 there are two words)

And if I need to setup OSCON or anything else