I2C
slave Multiplexed Display
(Turnkey
project)
Introduction
This project demonstrates a multiplexed display with
I2C interface.
The sub-circuits used in this project
are:
- 'I2C slave RAM'
- 'Display 4-dig 7-seg (com anode)
- '3-bit port'
The target device is a PIC16F872 with
crystal clock running at 4.0MHz.
The industry standard I2C bus opens
the way for modular design offering cross-platform
support and re-usable design. This project can be
used as a framework for other I2C slave devices and
can also be a sub-circuit in its own right, an example
of which is the 'I2C 4-dig mux display' sub-circuit.
Operation
Looking from the outside the I2C interface appears
as a 2-byte RAM device. The 4-digit multiplexed display
is updated by simply writing data to location 0 of
the I2C RAM. When the RAM is written to, it sets a
flag indicating that new data has arrived, the foreground
programme (main programme loop) detects this event
and carries out the required task, in this case, updating
the display.
The following operations can be carried
out when writing to the 'I2C slave RAM' device:
Address / Data / Operation
0 / 0 / Clear display
0 / 1 / Home cursor
0 / n / Print character to display i.e. '0123456789.-Er<space><CR>'
A read may be made from address 0 over
the I2C bus as confirmation of a successful write.
The 'I2C slave RAM' can be configured
to have more memory at design time and can have any
family address and any device address. The '3-bit
port' effectively overwrites the device address at
run time and this facilitates hardwired addressing
of the I2C. See 'ADD_' on the design sheet.
Application code
Below is the application code for this project. To
use it, select and copy (ctr-insert) the code below
and past it into a text editor and save as a 'C' file
in your working directory. You may also need to change
the build output path using 'Project | Options'
///////////////////////////////////////////////////////////////////////
//// AI2CMUXD.C ////
//// ////
//// Demo application of simple 4-digit multiplex 7-segment ////
//// display with i2c interface. ////
//// ////
//// Use the i2c interface to write digits to the display. ////
//// The i2c interface behaves as a 2 byte i2c slave RAM. ////
//// Writing data to address 0 will write a digit to the display. ////
//// See also sub-circuit 'I2C 4-Digit mux display' ////
//// ////
//// This program is an example of how your application code is ////
//// is organised. Note the #include "i2cmuxd.c", this include ////
//// file was generated by QuickBuilder and contains all ////
//// dirver code. ////
//// ////
//// This demo is intended for a PIC16F872 ////
//// Compile using CCS 'C' visit www.quickbuilder.co.uk/qb/ccs ////
///////////////////////////////////////////////////////////////////////
#include <16f872.H>
#fuses hs,wdt,noprotect,put,nowrt,nolvp
#include
#define PORTA 5
#define PORTB 6
#define PORTC 7
#define TRISA 0x85
#define TRISB 0x86
#define TRISC 0x87
#define RTCC_ZERO INT_TIMER0
#include "i2cmuxd.c"
#int_rtcc
void RTCC_ISR()
{
MUXD_1DO(); // refresh display
}
main() {
byte b;
bit_clear(*trisc,7); // test output
// initialise sub-circuits and rtcc interrupts
//--------------------------------------------
INIT_SUB_CIRCUITS();
setup_counters(RTCC_INTERNAL,RTCC_DIV_2);
enable_interrupts(RTCC_ZERO);
enable_interrupts(GLOBAL);
// I2C set device address
I2CSLRAM_1SETDADD( ADD_READ() );
// power up test display
// ---------------------
I2CSLRAM_1DISABLE();
printf(muxd_1putc,"8.8.8.8"); // all on for 1/2sec
for ( b=250; b!=0 ; b--) {delay_ms(2); restart_wdt();}
muxd_1clear(); // all off for 1/2sec
for ( b=250; b!=0 ; b--) {delay_ms(2); restart_wdt();}
I2CSLRAM_1ENABLE();
// main loop
//----------
while(1) {
restart_wdt();
// monitor i2c for updates
if ( I2CSLRAM_1UPDATE == 2) {
I2CSLRAM_1UPDATE = 0; // clear i2c update flag
if ( I2CSLRAM_1ADDR == 0 ) {
b = I2CSLRAM_1DATA[0];
if (b == 0 )
MUXD_1CLEAR();
else if (b == 1 )
MUXD_1CURHOME();
else
MUXD_1PUTC(b);
}
}
// poll i2c ram
I2CSLRAM_1DO();
}
}
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