 |
 |
| View previous topic :: View next topic |
| Author |
Message |
PicNewboy
Joined: 20 Apr 2005
Posts: 1
|
| From master to slave and back |
 Posted: Mon Apr 25, 2005 6:18 am |
 |
|
Hi everybody!I have a board with two 18F4525 and they are connected via 3 wires (Data,Clock and RB0).I want that one work like master and other like slave.After some independent operations I'd like that master became slave and slave master.It's possible?I've tried something like this but it doesn't work:
| Code: | #include <18f4525.h>
#device adc=10
#fuses H4,NOLVP,NOWDT,PUT,NOBROWNOUT
#use delay(clock=40000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
int get_com(int);
int get_frec(void);
void init_spi_M(void);
void init_spi_S(void);
//MASTER
int get_mpp(void);
void main(void)
{
int indicator;
int value;
int mpp_new,mpp_old;
int com1,com2,com3,f,D;
printf("SPI test start(MASTER).\r\n");
delay_ms(500);
while(TRUE){
if (PIN_B0){
init_spi_M();
mpp_old=get_mpp();
spi_write(indicator);
spi_write(value);
!(PIN_B0);
}
else{
init_spi_S();
spi_read(com1);
spi_read(com2);
spi_read(com3);
spi_read(f);
spi_read(D);
// mpp_new=get_mpp();
if (mpp_new>=mpp_old)
PIN_B0;
}
}
}
//SLAVE
void main(void)
{
int indicator;
int value;
int mpp_new,mpp_old;
int fase1,fase2,fase3;
int com1,com2,com3,f,D;
printf("SPI test start(SLAVE).\r\n");
delay_ms(500);
while(TRUE){
if (!(PIN_B0)){
init_spi_M();
com1=get_com(fase1);
com2=get_com(fase2);
com3=get_com(fase3);
f=get_frec();
spi_write(com1);
spi_write(com2);
spi_write(com3);
spi_write(f);
(PIN_B0);
}
else{
init_spi_S();
spi_read(indicator);
spi_read(value);
spi_read(com3);
if (D==1)
!(PIN_B0);
}
}
}
void init_spi_M(void)
{
setup_spi(SPI_MASTER | SPI_L_TO_H | SPI_CLK_DIV_16);
return;
}
void init_spi_S(void)
{
setup_spi(SPI_SLAVE| SPI_L_TO_H);
return;
}
|
Thank you. |
|
 |
DragonPIC
Joined: 11 Nov 2003
Posts: 118
|
|
| Posted: Mon Apr 25, 2005 2:18 pm |
|
|
Before I read your code too closely, have you tried using one a a slave and the other as a master and have it work? Then, did you switch and test again? Just to confirm they are both capable of being a master or a slave. Sanity checks always help before getting into the mess.
_________________
-Matt |
|
|
Ttelmah
Guest
|
|
| Posted: Mon Apr 25, 2005 2:36 pm |
|
|
First comment:
The statement:
if (PIN_B0){
Will allways evaluate as 'true'. PIN_B0, is a numeric value, which is used with the commands 'input', and 'output', to talk to the pins. You need to replace this with an if (input(PIN_B0)) statement to actually access the pin. The same is true where you try to access the pin by just putting a line 'PIN_B0'. Here you need 'output_bit(PIN_B0,1)' to set it , or use a '0' to clear it. To invert it, you need 'output_bit(PIN_B0,!input(PIN_B0))', or use the 'toggle' command (depending on the version of your compiler...).
What you describe, won't work. The problem is that the SPI itself uses three pins. there is CLK, and a data_in, and data_out line at each end. When operating to send data as a master, this chip would be using it's 'data_out' pin, while when expected to operate as a slave, it'd need to use it's 'data_in' pin. The same reversal wuld happen at the other end.
Consider instead using the I2C bus instead. The advantage here is that the bus only uses two pins for the transfer (being mono-directional, instead of transferring data simultaneaously in both directions), and these are 'open collector' drives, which removes a potential bus 'clash' if both chips try to be 'masters' at once. Program both chips as 'slaves', and only switch to being 'master' if you want to send something. Add a short delay after seeing the pin change, to verify that the bus is genuinely not in use. I have done this in the past with assembler, and it can be made to work OK, so should be possible.
Best Wishes |
|
|
DragonPIC
Joined: 11 Nov 2003
Posts: 118
|
|
| Posted: Wed Apr 27, 2005 8:07 am |
|
|
| Ttelmah wrote: | What you describe, won't work. The problem is that the SPI itself uses three pins. there is CLK, and a data_in, and data_out line at each end. When operating to send data as a master, this chip would be using it's 'data_out' pin, while when expected to operate as a slave, it'd need to use it's 'data_in' pin. The same reversal wuld happen at the other end.
Best Wishes |
This was the reason for my reply. Good programming technique is to start as small as possible first. Once that works, move on to the more complicated stuff. Verify that the bus is working in one configuration first before trying to switch master and slave. This helps you understand the real problem as well as making it easier for people in this forum to help you.
_________________
-Matt |
|
|
Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
|
|
| Posted: Wed Apr 27, 2005 10:46 am |
|
|
| You could use I2C to do it. |
|
|
PicNewboy
Joined: 20 Apr 2005
Posts: 1
|
| Sorry everybody! |
| Posted: Thu Apr 28, 2005 2:46 am |
|
|
| I didn't was clear in my question but I'm using 4 wires (1 clock,2 data and one between RB0 pins of pics).I have time limits so I have think that SPI were the best solution instead of I2C.Sorry again and thank you for the answers. |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
FAQ 
Search
Register
Profile 
Log in to check your private messages 
Log in
