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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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 Posted: Tue Aug 14, 2007 12:30 pm |
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Using i2c hardware mode for the Master. (Slave must always use H/W).
Also be aware that to make the code reliable, you may have to back off
the SCL frequency from the highest value that works in initial testing.
I didn't do any reliability tests. |
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Tim Bobbins
Guest
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| my results |
| Posted: Thu Aug 16, 2007 1:29 am |
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Here are my results with FORCE_HW enabled with the test code as found below. The test master code sends a character continuously to the slave. The slave returns the same character back to the master. The master code counts the number of times per second a successful reception is made:
FAST=100000
~1300 bytes per second
FAST=250000
~2900Bps
FAST=300000
~3300Bps
FAST=320000
~3400Bps
with FORCE_HW removed (software mode) the best I get is 2300Bps
Any idea why I cannot attain higher speeds past 320,000 and 350,000 for PCM programmer?
**slave code is the same as found in EX_SLAVE.C with the I2C line changed to:
#use i2c(SLAVE, SDA=PIN_C4, SCL=PIN_C3, address=0xa0, FORCE_HW, FAST=320000) **
**master code is as follows: **
| Code: | #include <16F876A.h>
#fuses HS // High speed external oscillator
#fuses PUT // Using the power up timer
#fuses NODEBUG // Do not use debug mode
#fuses NOBROWNOUT // Do not use brownout detect
#fuses NOLVP // Do not use low voltage programming
#fuses NOCPD // Do not use code protect
#fuses NOWRT // Do now use write protect
#use delay(clock=20M,oscillator)
#use rs232(STREAM=RS485_PORT,BRGH1OK,baud=115200, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
#use i2c(Master, sda=PIN_C4, scl=PIN_C3,FAST=350000) //FORCE_HW,
//RTC variables
#define XTAL_FREQUENCY 20000000
#define TIMER1_FREQUENCY (XTAL_FREQUENCY / 4) // 1 clock tick = 1 instr. cycle = crystal frequency / 4
int32 Ticker;
int8 Seconds=0;
//====================================
#int_TIMER1
void TIMER1_isr()
{
Ticker -= 65536; // Decrement ticker by clocks per interrupt
if ( Ticker < 65536 ) // If second has expired
{ Ticker += TIMER1_FREQUENCY; // Increment ticker by clocks per second
seconds++; // Increment number of seconds
}
}
////////////////////////////////////////////////////////////////////////////////
// Initialize RTC
////////////////////////////////////////////////////////////////////////////////
void Initialize_RTC(void)
{
Ticker = TIMER1_FREQUENCY; // initialize clock counter to number of clocks per second
setup_timer_1( T1_INTERNAL | T1_DIV_BY_1 ); // initialize 16-bit Timer1 to interrupt
// exactly every 65536 clock cycles
// (about 76 times per second)
enable_interrupts( INT_TIMER1 ); // Start RTC
}
void main()
{
int8 data,prev_second=-1;
int32 sent=0,received=0;
printf("START\n\r");
Initialize_RTC();
enable_interrupts( GLOBAL );
//have second counter increment, and show the findings
while(1)
{
if (seconds != prev_second)
{
prev_second = seconds;
output_toggle(PIN_A1);
printf("Time:%u Sent:%Lu Rcvd:%Lu\n\r",seconds,sent,received);
sent=0;
received=0;
}
// Write the letter 'B' to the slave board.
i2c_start();
i2c_write(0xA0);
i2c_write(0x00);
i2c_write('B');
i2c_stop();
sent++;
// Read from the slave board and display the data.
i2c_start();
i2c_write(0xA0);
i2c_write(0x00);
i2c_start();
i2c_write(0xA1);
data = i2c_read(0);
i2c_stop();
if (data=='B') received++; //increment counter
}
} |
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Tim Bobbins
Guest
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| any takers? |
| Posted: Sun Aug 19, 2007 10:10 pm |
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| Can anyone help to shine some light on why we cant achieve higher speeds above 300k? |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Aug 19, 2007 10:43 pm |
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Microchip doesn't say that it will work at 400 KHz. In fact, they hint
that it will not. Here's a note from the MSSP errata:
| Quote: | Note 1: The I2C™ interface does not conform to the 400 kHz I2C
specification (which applies to rates greater than 100 kHz) in all details,
but may be used with care where higher rates are required by the
application. |
http://ww1.microchip.com/downloads/en/DeviceDoc/80131e.pdf
I suggest that you contact a Microchip FAE and ask if they know how
fast you can run an i2c slave. If they say 400 KHz, then ask them for
sample code. It will likely be MPASM code, but you can still test it,
and if it works, maybe it can be translated to C. |
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Tim Bobbins
Guest
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| microchip response |
| Posted: Wed Aug 22, 2007 11:49 am |
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This is the response I received back from Microchip:
| Quote: | Per the Errata you should be able to achieve the 400kHz rate but it cautions you that the I2C module does not meet the 400kHz specifications of I2C.
Unfortunately all the sample code we have for I2C is in regards to Master mode communication.
Regards. |
So, I will search on the internet to see if someone else has implemented some fast-spec assembly I2C code - or just deal with the 300k speed. Will also look into whether changing to a 18-series chip will make any difference. The speed is of critical importance |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Wed Aug 22, 2007 12:32 pm |
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| Quote: | | The speed is of critical importance |
Íf speed is so critical, how about changing the bus? The SPI bus is much faster, up to 10megabit on a 40MHz processor. Less communication overhead too, so less stress on your processor. Disadvantage is that it uses 1 more communication line plus an additional chip select line for every connected device. |
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