Subject:
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GP2D02 Interface Question?
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Wed, 13 Jan 1999 14:34:53 GMT
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Original-From:
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Lewis Patterson <lewis@bsc.edu{Spamcake}>
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Viewed:
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977 times
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Attached below is IC code for a GP2D02 rangefinder. This is a slightly
enhanced version of code from Bjorn Astrand. My question relates to
the use of TMSK1 in the code. From reading various M69HC11 documents,
I think (???) that I know what bits are being set but I do NOT understand
why this is being done. If someone would help me understand the
necessity of using TMSK1 for this routine, I would be grateful. If you
see other problems in the code, please let me know. Thanks!
/*----------------------------------------------------------------------*/
/* sharp.c - Interface for Sharp GP2D02 infrared rangefinder. This
routine is a modification of code written by Bjorn Astrand (see
http://www.hh.se/staff/bjorn/download/).
The GP2D02 must be connected with Vin attached to MISO and Vout
attached to MOSI (port D pins).
Note: Vin is connected to MISO through a simple voltage divider
network to insure that it does not exceed 3 volts. A crude picture
of the network is shown below.
MISO -------R1(1K)---------------------- Vin (GP2D02)
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R2(1K)
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-----
---
-
*/
/*---------------------------------------------------------------------*/
#undef DEBUG
int sharp(){
#define TMSK1 0x1022
#define PORTD 0x1008
#define DDRD 0x1009
int result;
int mask= 8;
int bit0,bit1,bit2,bit3,bit4,bit5,bit6,bit7;
long t;
/* Define D port output pin which is connected to Vin of GP2D02. */
poke(DDRD,0b00000100);
/* Raise Vin to reset the GP2D02. */
poke(PORTD,0b00000100);
/* Let that signal remain high for a short interval (safety). */
msleep(2L);
/* Drop Vin to trigger a measurement by GP2D02. */
poke(PORTD,0b00000000);
/* Wait a max of 70 msecs or until Vout from GP2D02 goes high. */
t= mseconds()+70L;
while(mseconds() < t){
/* Break the delay loop if we see an input signal. */
if((peek(PORTD)&mask) == 1)break;
msleep(2L);
}
/* Setup the TMSK1 register. */
poke(TMSK1,0b00001100); /* ??? */
/* Repeatedly raise and lower Vin to gate the 8 bits
of data from the GP2D02; save each bit. */
poke(PORTD,0b00000100);
poke(PORTD,0b00000000);
bit0= peek(PORTD);
poke(PORTD,0b00000100);
poke(PORTD,0b00000000);
bit1= peek(PORTD);
poke(PORTD,0b00000100);
poke(PORTD,0b00000000);
bit2= peek(PORTD);
poke(PORTD,0b00000100);
poke(PORTD,0b00000000);
bit3= peek(PORTD);
poke(PORTD,0b00000100);
poke(PORTD,0b00000000);
bit4= peek(PORTD);
poke(PORTD,0b00000100);
poke(PORTD,0b00000000);
bit5= peek(PORTD);
poke(PORTD,0b00000100);
poke(PORTD,0b00000000);
bit6= peek(PORTD);
poke(PORTD,0b00000100);
poke(PORTD,0b00000000);
bit7= peek(PORTD);
/* Restore Vin to HIGH state. */
poke(PORTD,0b00000100);
/* Reset the TMSK1 register. */
poke(TMSK1,0b00011100); /* ??? */
/* Combine those bits into an integer result. */
result= (bit0&mask)*16+(bit1&mask)*8+(bit2&mask)*4+(bit3&mask)*2+
(bit4&mask)+(bit5&mask)/2+(bit6&mask)/4+(bit7&mask)/8;
#ifdef DEBUG
printf("%b\n",result);
#endif
/* Return the result. */
return result;
}
void sharp_testing(){
while(!stop_button()){
printf("%d\n",sharp());
}
beep();
}
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