Servo - July 2009

 //snooze
 //wait for Break sequence
 // to complete
bytein = RCREG; //discard the byte,
 // clear RCIF flag
while(ABDEN); //measure the chirp
bytein = RCREG; //discard the byte,
 // clear RCIF flag
enable_RXint; //get ready for real data

SLEEP();
while(WUE);

//wait for incoming PID
while(!(CharInQueue()));
pid_in = recvchar(); //retrieve PID
id_in = pid_in & 0x3F;  //get identifier
if(id_in == 0x02)
{

//number of data bytes in response
lin_buf[msg_len] = 3;
//used to compute frame checksum
lin_buf[id_loc] = pid_in;
lin_buf[msg_loc] = 0x11;
lin_buf[msg_loc+1] = 0x22;
lin_buf[msg_loc+2] = 0x33;
//enhanced checksum calculation
checksum = lin_buf[id_loc];
for(i=0;i<lin_buf[msg_len];++i)
{

// data

checksum = checksum +
 lin_buf[msg_loc+i];

}
//where to store frame checksum
chksum_loc = msg_loc + 3;
lin_buf[chksum_loc] =
 ~(checksum & 0x00FF);

//add checksum ato length
lin_buf[msg_len] = lin_buf[msg_len]+1;
LIN_TX;  //place MCP2201 in Tx mode
//SEND RESPONSE
for(i=0;i<lin_buf[msg_len];++i)
{

sendchar(lin_buf[msg_loc+i]);

}
do{
 LED1 ^= 1;
 sdelay1(2);

//kill time

Microchip — www.microchip.com

LIN Serial Analyzer MCP2021 PIC18F2620 MPLAB REAL ICE MPLAB ICD2 HI-TECH PICC- 18 PRO C Compiler LIN Node Printed Circuit Board

Sources

}while(1);

There should be no mystery surrounding the code preceding the if(id_in==0x02) statement. You shouldn’t have any trouble following the rest of the slave response code either as we’ve only adjusted the response transmission routine. With the help of the LIN Serial Analyzer, I can offer you the visual results of the slave response code in Screenshot 4.

You are a LIN Master

The LIN-influenced hardware and software elements we have discussed can be used to build a number of LIN slave node variants, as well as a LIN master node. The LIN node hardware we assembled can be used in applications using the official LIN Specifications.

However, I think that those of you that put our LIN hardware to work will come up with your own “specifications” and use the LIN frame’s PID and eight response bytes to your robotic advantage. SV

Fred Eady can be reached via email at fred@edtp.com

STEER WINNING ROBOTS WITHOUT SERVOS!

Perform proportional speed, direction, and steering with only two Radio/Control channels for vehicles using two separate brush-type electric motors mounted right and left with our mixing RDFR dual speed control. Used in many successful competitive robots. Single joystick operation: up goes straight ahead, down is reverse. Pure right or left twirls vehicle as motors turn opposite directions. In between stick positions completely proportional. Plugs in like a servo to your Futaba, JR, Hitec, or similar radio. Compatible with gyro steering stabilization. Various volt and amp sizes available. The RDFR47E 55V 75A per motor unit pictured above. www.vantec.com