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lacolo
Joined: 10 Mar 2006
Posts: 15
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| issues with multiple LCDs and the "ready" flag |
 Posted: Wed Apr 05, 2006 12:25 am |
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Hello,
I am working on an installation with one PIC18F452 driving 10 LCDs (VK2220 - http://www.wrighthobbies.net/datasheets/VK2220.pdf)
I've modified the LCD.c to be able to communicate with various LCD panels. That is working fine, but I have an issue I want to be able to prevent.
Currently, if one LCD fails (in hardware), the entire program will stall.
This is because the LCD_sendByte() routine in LCD.c (modified) waits for a "ready" flag before it communicates with a panel. If that panel doesn't respond, the program doesn't progress.
Any suggestions on what I can do on the hardware side, so that a "lack of response" doesn't stall the program? OR, any suggestions on the software side on some if statement to precede LCD_sendByte()?
Thanks!
//Cynthia |
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sjbaxter
Joined: 26 Jan 2006
Posts: 141
Location: Cheshire, UK
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| Posted: Wed Apr 05, 2006 3:06 am |
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You could change the send byte function to take a timeout value (in microseconds) and a return flag indicating success or a timeout (failure).
| Code: | int1 lcd_send_byte( BYTE address, BYTE n, int8 timeout ) {
int8 count;
lcd.rs = 0;
count = 0;
while ( bit_test(lcd_read_byte(),7) )
{
delay_us(1);
count++;
if (count >= timeout )
{
// timed out ...
return false;
}
};
lcd.rs = address;
delay_cycles(1);
lcd.rw = 0;
delay_cycles(1);
lcd.enable = 0;
lcd_send_nibble(n >> 4);
lcd_send_nibble(n & 0xf);
// success
return true;
}
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you may also want to change the lcd_getc to use the same timeout mechanism.
In this example I have defined the timeout as as int8 so a maximum of 255us is possible, you chould change the delay_us to use delay_ms or increase the granularity from 1us to 10 or 100 us by changing the delay_us(xx) statement. It all depends on how long your application can tolerate the function stalling the program (in the worst case of a display failing to respond).
_________________
Regards,
Simon. |
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